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 $53.51   12.148%   $60.0104   $60.01   $60.00   $60.00  
  Purchase #2 $97.66   12.294%   $109.6663   $109.67   $109.65   $109.70  
  Purchase #3 $166.47   7.634%   $179.1783   $179.18   $179.20   $179.20  
  Purchase #4 $92.76   9.332%   $101.4164   $101.42   $101.40   $101.40  
  Purchase #5 $92.88   12.759%   $104.7306   $104.73   $104.75   $104.70  
  Purchase #6 $205.87   3.834%   $213.7631   $213.76   $213.75   $213.80  
  Purchase #7 $225.89   7.633%   $243.1322   $243.13   $243.15   $243.10  
  7 purchase totals = $935.04       $1,011.8973   $1,011.90   $1,011.90   $1,011.90