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 $125.63   8.215%   $135.9505   $135.95   $135.95   $136.00  
  Purchase #2 $237.88   12.570%   $267.7815   $267.78   $267.80   $267.80  
  Purchase #3 $167.97   5.740%   $177.6115   $177.61   $177.60   $177.60  
  Purchase #4 $153.42   4.507%   $160.3346   $160.33   $160.35   $160.30  
  Purchase #5 $21.96   9.528%   $24.0523   $24.05   $24.05   $24.10  
  Purchase #6 $162.39   5.445%   $171.2321   $171.23   $171.25   $171.20  
  Purchase #7 $107.65   8.529%   $116.8315   $116.83   $116.85   $116.80  
  7 purchase totals = $976.90       $1,053.7940   $1,053.78   $1,053.85   $1,053.80