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 $152.60   6.123%   $161.9437   $161.94   $161.95   $161.90  
  Purchase #2 $210.93   10.471%   $233.0165   $233.02   $233.00   $233.00  
  Purchase #3 $185.31   7.516%   $199.2379   $199.24   $199.25   $199.20  
  Purchase #4 $199.76   11.396%   $222.5246   $222.52   $222.50   $222.50  
  Purchase #5 $103.27   3.207%   $106.5819   $106.58   $106.60   $106.60  
  Purchase #6 $68.88   10.678%   $76.235   $76.24   $76.25   $76.20  
  Purchase #7 $149.60   4.763%   $156.7254   $156.73   $156.75   $156.70  
  7 purchase totals = $1,070.35       $1,156.2650   $1,156.27   $1,156.30   $1,156.10