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 $58.87   10.714%   $65.1773   $65.18   $65.20   $65.20  
  Purchase #2 $203.58   10.526%   $225.0088   $225.01   $225.00   $225.00  
  Purchase #3 $203.32   5.153%   $213.7971   $213.80   $213.80   $213.80  
  Purchase #4 $13.95   12.231%   $15.6562   $15.66   $15.65   $15.70  
  Purchase #5 $69.93   7.411%   $75.1125   $75.11   $75.10   $75.10  
  Purchase #6 $201.49   7.729%   $217.0632   $217.06   $217.05   $217.10  
  Purchase #7 $245.47   11.452%   $273.5812   $273.58   $273.60   $273.60  
  7 purchase totals = $996.61       $1,085.3963   $1,085.40   $1,085.40   $1,085.50