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 $235.28   5.281%   $247.7051   $247.71   $247.70   $247.70  
  Purchase #2 $201.35   4.351%   $210.1107   $210.11   $210.10   $210.10  
  Purchase #3 $108.37   5.601%   $114.4398   $114.44   $114.45   $114.40  
  Purchase #4 $168.93   5.692%   $178.5455   $178.55   $178.55   $178.50  
  Purchase #5 $59.39   12.608%   $66.8779   $66.88   $66.90   $66.90  
  Purchase #6 $39.52   13.583%   $44.888   $44.89   $44.90   $44.90  
  Purchase #7 $160.31   7.252%   $171.9357   $171.94   $171.95   $171.90  
  7 purchase totals = $973.15       $1,034.5027   $1,034.52   $1,034.55   $1,034.40