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 $82.36   9.392%   $90.0953   $90.10   $90.10   $90.10  
  Purchase #2 $126.93   5.719%   $134.1891   $134.19   $134.20   $134.20  
  Purchase #3 $186.65   12.685%   $210.3266   $210.33   $210.35   $210.30  
  Purchase #4 $200.34   6.288%   $212.9374   $212.94   $212.95   $212.90  
  Purchase #5 $133.92   9.398%   $146.5058   $146.51   $146.50   $146.50  
  Purchase #6 $112.79   7.273%   $120.9932   $120.99   $121.00   $121.00  
  Purchase #7 $248.99   10.191%   $274.3646   $274.36   $274.35   $274.40  
  7 purchase totals = $1,091.98       $1,189.4120   $1,189.42   $1,189.45   $1,189.40