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 $246.81   12.210%   $276.9455   $276.95   $276.95   $276.90  
  Purchase #2 $126.54   8.798%   $137.673   $137.67   $137.65   $137.70  
  Purchase #3 $28.59   13.656%   $32.4943   $32.49   $32.50   $32.50  
  Purchase #4 $137.37   8.557%   $149.1248   $149.12   $149.10   $149.10  
  Purchase #5 $101.33   12.557%   $114.054   $114.05   $114.05   $114.10  
  Purchase #6 $181.38   8.355%   $196.5343   $196.53   $196.55   $196.50  
  Purchase #7 $122.51   6.417%   $130.3715   $130.37   $130.35   $130.40  
  7 purchase totals = $944.53       $1,037.1974   $1,037.18   $1,037.15   $1,037.20