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 $235.68   13.516%   $267.5345   $267.53   $267.55   $267.50  
  Purchase #2 $224.37   8.590%   $243.6434   $243.64   $243.65   $243.60  
  Purchase #3 $142.40   9.140%   $155.4154   $155.42   $155.40   $155.40  
  Purchase #4 $167.30   6.854%   $178.7667   $178.77   $178.75   $178.80  
  Purchase #5 $14.88   11.319%   $16.5643   $16.56   $16.55   $16.60  
  Purchase #6 $241.81   6.253%   $256.9304   $256.93   $256.95   $256.90  
  Purchase #7 $192.67   12.243%   $216.2586   $216.26   $216.25   $216.30  
  7 purchase totals = $1,219.11       $1,335.1133   $1,335.11   $1,335.10   $1,335.10