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 $119.73   11.842%   $133.9084   $133.91   $133.90   $133.90  
  Purchase #2 $246.52   9.305%   $269.4587   $269.46   $269.45   $269.50  
  Purchase #3 $39.65   8.728%   $43.1107   $43.11   $43.10   $43.10  
  Purchase #4 $197.49   6.325%   $209.9812   $209.98   $210.00   $210.00  
  Purchase #5 $190.35   13.701%   $216.4299   $216.43   $216.45   $216.40  
  Purchase #6 $229.81   13.395%   $260.593   $260.59   $260.60   $260.60  
  Purchase #7 $246.54   5.761%   $260.7432   $260.74   $260.75   $260.70  
  7 purchase totals = $1,270.09       $1,394.2251   $1,394.22   $1,394.25   $1,394.20