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 $237.49   11.663%   $265.1885   $265.19   $265.20   $265.20  
  Purchase #2 $164.34   8.846%   $178.8775   $178.88   $178.90   $178.90  
  Purchase #3 $134.32   9.281%   $146.7862   $146.79   $146.80   $146.80  
  Purchase #4 $49.42   8.465%   $53.6034   $53.60   $53.60   $53.60  
  Purchase #5 $136.51   10.299%   $150.5692   $150.57   $150.55   $150.60  
  Purchase #6 $176.59   11.726%   $197.2969   $197.30   $197.30   $197.30  
  Purchase #7 $212.91   3.482%   $220.3235   $220.32   $220.30   $220.30  
  7 purchase totals = $1,111.58       $1,212.6452   $1,212.65   $1,212.65   $1,212.70