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 $83.76   10.711%   $92.7315   $92.73   $92.75   $92.70  
  Purchase #2 $147.82   13.771%   $168.1763   $168.18   $168.20   $168.20  
  Purchase #3 $121.59   3.571%   $125.932   $125.93   $125.95   $125.90  
  Purchase #4 $177.92   13.277%   $201.5424   $201.54   $201.55   $201.50  
  Purchase #5 $250.95   10.143%   $276.4039   $276.40   $276.40   $276.40  
  Purchase #6 $157.87   6.658%   $168.381   $168.38   $168.40   $168.40  
  Purchase #7 $214.28   10.449%   $236.6701   $236.67   $236.65   $236.70  
  7 purchase totals = $1,154.19       $1,269.8372   $1,269.83   $1,269.90   $1,269.80