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 $122.60   11.622%   $136.8486   $136.85   $136.85   $136.80  
  Purchase #2 $178.51   12.788%   $201.3379   $201.34   $201.35   $201.30  
  Purchase #3 $187.65   6.582%   $200.0011   $200.00   $200.00   $200.00  
  Purchase #4 $22.87   4.459%   $23.8898   $23.89   $23.90   $23.90  
  Purchase #5 $87.29   7.607%   $93.9302   $93.93   $93.95   $93.90  
  Purchase #6 $121.59   5.136%   $127.8349   $127.83   $127.85   $127.80  
  Purchase #7 $236.60   7.752%   $254.9412   $254.94   $254.95   $254.90  
  7 purchase totals = $957.11       $1,038.7837   $1,038.78   $1,038.85   $1,038.60