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 $52.52   9.337%   $57.4238   $57.42   $57.40   $57.40  
  Purchase #2 $242.54   8.288%   $262.6417   $262.64   $262.65   $262.60  
  Purchase #3 $88.31   7.676%   $95.0887   $95.09   $95.10   $95.10  
  Purchase #4 $163.70   7.314%   $175.673   $175.67   $175.65   $175.70  
  Purchase #5 $91.34   13.648%   $103.8061   $103.81   $103.80   $103.80  
  Purchase #6 $132.94   8.367%   $144.0631   $144.06   $144.05   $144.10  
  Purchase #7 $22.35   8.756%   $24.307   $24.31   $24.30   $24.30  
  7 purchase totals = $793.70       $863.0034   $863.00   $862.95   $863.00