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 $92.36   10.199%   $101.7798   $101.78   $101.80   $101.80  
  Purchase #2 $200.76   11.405%   $223.6567   $223.66   $223.65   $223.70  
  Purchase #3 $165.93   11.342%   $184.7498   $184.75   $184.75   $184.70  
  Purchase #4 $216.99   11.756%   $242.4993   $242.50   $242.50   $242.50  
  Purchase #5 $86.96   5.787%   $91.9924   $91.99   $92.00   $92.00  
  Purchase #6 $233.69   4.818%   $244.9492   $244.95   $244.95   $244.90  
  Purchase #7 $170.59   13.808%   $194.1451   $194.15   $194.15   $194.10  
  7 purchase totals = $1,167.28       $1,283.7723   $1,283.78   $1,283.80   $1,283.70