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 $204.81   10.560%   $226.4379   $226.44   $226.45   $226.40  
  Purchase #2 $45.79   11.775%   $51.1818   $51.18   $51.20   $51.20  
  Purchase #3 $45.98   5.834%   $48.6625   $48.66   $48.65   $48.70  
  Purchase #4 $180.77   12.351%   $203.0969   $203.10   $203.10   $203.10  
  Purchase #5 $223.96   3.543%   $231.8949   $231.89   $231.90   $231.90  
  Purchase #6 $158.25   7.154%   $169.5712   $169.57   $169.55   $169.60  
  Purchase #7 $83.49   13.826%   $95.0333   $95.03   $95.05   $95.00  
  7 purchase totals = $943.05       $1,025.8785   $1,025.87   $1,025.90   $1,025.90