Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $106.54   11.799%   $119.1107   $119.11   $119.10   $119.10  
  Purchase #2 $200.57   8.333%   $217.2835   $217.28   $217.30   $217.30  
  Purchase #3 $245.43   6.203%   $260.654   $260.65   $260.65   $260.70  
  Purchase #4 $151.41   10.776%   $167.7259   $167.73   $167.75   $167.70  
  Purchase #5 $221.29   10.401%   $244.3064   $244.31   $244.30   $244.30  
  Purchase #6 $121.71   10.523%   $134.5175   $134.52   $134.50   $134.50  
  Purchase #7 $230.82   8.598%   $250.6659   $250.67   $250.65   $250.70  
  7 purchase totals = $1,277.77       $1,394.2639   $1,394.27   $1,394.25   $1,394.30