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 $228.39   6.818%   $243.9616   $243.96   $243.95   $244.00  
  Purchase #2 $168.75   7.682%   $181.7134   $181.71   $181.70   $181.70  
  Purchase #3 $213.75   6.569%   $227.7912   $227.79   $227.80   $227.80  
  Purchase #4 $11.77   6.484%   $12.5332   $12.53   $12.55   $12.50  
  Purchase #5 $148.87   8.709%   $161.8351   $161.84   $161.85   $161.80  
  Purchase #6 $172.61   9.261%   $188.5954   $188.60   $188.60   $188.60  
  Purchase #7 $17.88   11.688%   $19.9698   $19.97   $19.95   $20.00  
  7 purchase totals = $962.02       $1,036.3997   $1,036.40   $1,036.40   $1,036.40