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 $41.51   13.223%   $46.9989   $47.00   $47.00   $47.00  
  Purchase #2 $234.32   13.428%   $265.7845   $265.78   $265.80   $265.80  
  Purchase #3 $248.95   13.822%   $283.3599   $283.36   $283.35   $283.40  
  Purchase #4 $11.88   7.603%   $12.7832   $12.78   $12.80   $12.80  
  Purchase #5 $7.29   5.610%   $7.699   $7.70   $7.70   $7.70  
  Purchase #6 $8.92   6.738%   $9.521   $9.52   $9.50   $9.50  
  Purchase #7 $238.48   9.160%   $260.3248   $260.32   $260.30   $260.30  
  7 purchase totals = $791.35       $886.4713   $886.46   $886.45   $886.50