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 $138.54   8.717%   $150.6165   $150.62   $150.60   $150.60  
  Purchase #2 $152.38   6.414%   $162.1537   $162.15   $162.15   $162.20  
  Purchase #3 $124.68   4.610%   $130.4277   $130.43   $130.45   $130.40  
  Purchase #4 $249.95   5.592%   $263.9272   $263.93   $263.95   $263.90  
  Purchase #5 $212.59   4.506%   $222.1693   $222.17   $222.15   $222.20  
  Purchase #6 $53.86   8.209%   $58.2814   $58.28   $58.30   $58.30  
  Purchase #7 $243.29   11.408%   $271.0445   $271.04   $271.05   $271.00  
  7 purchase totals = $1,175.29       $1,258.6203   $1,258.62   $1,258.65   $1,258.60