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 $48.94   4.210%   $51.0004   $51.00   $51.00   $51.00  
  Purchase #2 $183.65   9.472%   $201.0453   $201.05   $201.05   $201.00  
  Purchase #3 $24.63   5.246%   $25.9221   $25.92   $25.90   $25.90  
  Purchase #4 $192.69   4.139%   $200.6654   $200.67   $200.65   $200.70  
  Purchase #5 $59.79   4.686%   $62.5918   $62.59   $62.60   $62.60  
  Purchase #6 $244.34   9.442%   $267.4106   $267.41   $267.40   $267.40  
  Purchase #7 $201.93   5.206%   $212.4425   $212.44   $212.45   $212.40  
  7 purchase totals = $955.97       $1,021.0781   $1,021.08   $1,021.05   $1,021.00