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 $23.89   9.275%   $26.1058   $26.11   $26.10   $26.10  
  Purchase #2 $149.76   7.345%   $160.7599   $160.76   $160.75   $160.80  
  Purchase #3 $61.37   6.659%   $65.4566   $65.46   $65.45   $65.50  
  Purchase #4 $100.95   8.635%   $109.667   $109.67   $109.65   $109.70  
  Purchase #5 $65.37   9.217%   $71.3952   $71.40   $71.40   $71.40  
  Purchase #6 $96.81   5.456%   $102.092   $102.09   $102.10   $102.10  
  Purchase #7 $201.34   4.783%   $210.9701   $210.97   $210.95   $211.00  
  7 purchase totals = $699.49       $746.4466   $746.46   $746.40   $746.60