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 $138.32   11.823%   $154.6736   $154.67   $154.65   $154.70  
  Purchase #2 $236.63   12.652%   $266.5684   $266.57   $266.55   $266.60  
  Purchase #3 $204.79   3.415%   $211.7836   $211.78   $211.80   $211.80  
  Purchase #4 $156.87   7.419%   $168.5082   $168.51   $168.50   $168.50  
  Purchase #5 $102.93   7.269%   $110.412   $110.41   $110.40   $110.40  
  Purchase #6 $215.71   10.861%   $239.1383   $239.14   $239.15   $239.10  
  Purchase #7 $51.51   11.676%   $57.5243   $57.52   $57.50   $57.50  
  7 purchase totals = $1,106.76       $1,208.6084   $1,208.60   $1,208.55   $1,208.60