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 $94.30   11.289%   $104.9455   $104.95   $104.95   $104.90  
  Purchase #2 $227.85   9.837%   $250.2636   $250.26   $250.25   $250.30  
  Purchase #3 $46.51   9.187%   $50.7829   $50.78   $50.80   $50.80  
  Purchase #4 $177.98   7.421%   $191.1879   $191.19   $191.20   $191.20  
  Purchase #5 $65.45   12.828%   $73.8459   $73.85   $73.85   $73.80  
  Purchase #6 $161.56   9.480%   $176.8759   $176.88   $176.90   $176.90  
  Purchase #7 $180.69   3.855%   $187.6556   $187.66   $187.65   $187.70  
  7 purchase totals = $954.34       $1,035.5573   $1,035.57   $1,035.60   $1,035.60