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 $131.34   12.515%   $147.7772   $147.78   $147.80   $147.80  
  Purchase #2 $191.95   13.388%   $217.6483   $217.65   $217.65   $217.60  
  Purchase #3 $212.43   7.443%   $228.2412   $228.24   $228.25   $228.20  
  Purchase #4 $216.94   13.527%   $246.2855   $246.29   $246.30   $246.30  
  Purchase #5 $240.93   13.704%   $273.947   $273.95   $273.95   $273.90  
  Purchase #6 $86.50   5.191%   $90.9902   $90.99   $91.00   $91.00  
  Purchase #7 $156.51   12.669%   $176.3383   $176.34   $176.35   $176.30  
  7 purchase totals = $1,236.60       $1,381.2277   $1,381.24   $1,381.30   $1,381.10