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 $181.48   13.398%   $205.7947   $205.79   $205.80   $205.80  
  Purchase #2 $13.40   5.409%   $14.1248   $14.12   $14.10   $14.10  
  Purchase #3 $185.36   13.685%   $210.7265   $210.73   $210.75   $210.70  
  Purchase #4 $42.36   7.812%   $45.6692   $45.67   $45.65   $45.70  
  Purchase #5 $249.38   6.244%   $264.9513   $264.95   $264.95   $265.00  
  Purchase #6 $66.74   11.700%   $74.5486   $74.55   $74.55   $74.50  
  Purchase #7 $225.82   8.500%   $245.0147   $245.01   $245.00   $245.00  
  7 purchase totals = $964.54       $1,060.8298   $1,060.82   $1,060.80   $1,060.80