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 $247.96   11.609%   $276.7457   $276.75   $276.75   $276.70  
  Purchase #2 $145.63   3.309%   $150.4489   $150.45   $150.45   $150.40  
  Purchase #3 $144.51   3.203%   $149.1387   $149.14   $149.15   $149.10  
  Purchase #4 $216.65   11.485%   $241.5323   $241.53   $241.55   $241.50  
  Purchase #5 $144.85   13.537%   $164.4583   $164.46   $164.45   $164.50  
  Purchase #6 $146.78   10.219%   $161.7794   $161.78   $161.80   $161.80  
  Purchase #7 $47.96   3.178%   $49.4842   $49.48   $49.50   $49.50  
  7 purchase totals = $1,094.34       $1,193.5875   $1,193.59   $1,193.65   $1,193.50