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 $244.25   13.102%   $276.2516   $276.25   $276.25   $276.30  
  Purchase #2 $80.92   5.231%   $85.1529   $85.15   $85.15   $85.20  
  Purchase #3 $245.66   5.753%   $259.7928   $259.79   $259.80   $259.80  
  Purchase #4 $232.75   5.817%   $246.2891   $246.29   $246.30   $246.30  
  Purchase #5 $204.52   9.553%   $224.0578   $224.06   $224.05   $224.10  
  Purchase #6 $79.44   9.844%   $87.2601   $87.26   $87.25   $87.30  
  Purchase #7 $214.99   5.633%   $227.1004   $227.10   $227.10   $227.10  
  7 purchase totals = $1,302.53       $1,405.9047   $1,405.90   $1,405.90   $1,406.10