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 $149.57   13.324%   $169.4987   $169.50   $169.50   $169.50  
  Purchase #2 $120.54   3.671%   $124.965   $124.97   $124.95   $125.00  
  Purchase #3 $243.28   7.315%   $261.0759   $261.08   $261.10   $261.10  
  Purchase #4 $108.66   6.801%   $116.05   $116.05   $116.05   $116.10  
  Purchase #5 $126.96   5.822%   $134.3516   $134.35   $134.35   $134.40  
  Purchase #6 $155.45   6.868%   $166.1263   $166.13   $166.15   $166.10  
  Purchase #7 $114.35   5.219%   $120.3179   $120.32   $120.30   $120.30  
  7 purchase totals = $1,018.81       $1,092.3854   $1,092.40   $1,092.40   $1,092.50