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 $189.93   7.116%   $203.4454   $203.45   $203.45   $203.40  
  Purchase #2 $118.65   6.210%   $126.0182   $126.02   $126.00   $126.00  
  Purchase #3 $14.38   9.133%   $15.6933   $15.69   $15.70   $15.70  
  Purchase #4 $100.36   9.144%   $109.5369   $109.54   $109.55   $109.50  
  Purchase #5 $205.92   11.198%   $228.9789   $228.98   $229.00   $229.00  
  Purchase #6 $62.28   4.284%   $64.9481   $64.95   $64.95   $64.90  
  Purchase #7 $235.99   13.299%   $267.3743   $267.37   $267.35   $267.40  
  7 purchase totals = $927.51       $1,015.9951   $1,016.00   $1,016.00   $1,015.90