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 $243.82   9.211%   $266.2783   $266.28   $266.30   $266.30  
  Purchase #2 $171.42   13.427%   $194.4366   $194.44   $194.45   $194.40  
  Purchase #3 $75.29   10.261%   $83.0155   $83.02   $83.00   $83.00  
  Purchase #4 $63.58   11.540%   $70.9171   $70.92   $70.90   $70.90  
  Purchase #5 $88.72   8.434%   $96.2026   $96.20   $96.20   $96.20  
  Purchase #6 $132.98   11.818%   $148.6956   $148.70   $148.70   $148.70  
  Purchase #7 $193.45   5.688%   $204.4534   $204.45   $204.45   $204.50  
  7 purchase totals = $969.26       $1,063.9991   $1,064.01   $1,064.00   $1,064.00