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 $135.46   12.555%   $152.467   $152.47   $152.45   $152.50  
  Purchase #2 $215.31   9.571%   $235.9173   $235.92   $235.90   $235.90  
  Purchase #3 $204.98   9.272%   $223.9857   $223.99   $224.00   $224.00  
  Purchase #4 $93.25   11.293%   $103.7807   $103.78   $103.80   $103.80  
  Purchase #5 $51.64   13.465%   $58.5933   $58.59   $58.60   $58.60  
  Purchase #6 $41.52   12.715%   $46.7993   $46.80   $46.80   $46.80  
  Purchase #7 $222.28   5.253%   $233.9564   $233.96   $233.95   $234.00  
  7 purchase totals = $964.44       $1,055.4997   $1,055.51   $1,055.50   $1,055.60