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 $156.59   4.560%   $163.7305   $163.73   $163.75   $163.70  
  Purchase #2 $241.87   10.353%   $266.9108   $266.91   $266.90   $266.90  
  Purchase #3 $209.54   12.279%   $235.2694   $235.27   $235.25   $235.30  
  Purchase #4 $64.31   7.604%   $69.2001   $69.20   $69.20   $69.20  
  Purchase #5 $142.58   6.426%   $151.7422   $151.74   $151.75   $151.70  
  Purchase #6 $210.93   12.388%   $237.06   $237.06   $237.05   $237.10  
  Purchase #7 $88.78   6.824%   $94.8383   $94.84   $94.85   $94.80  
  7 purchase totals = $1,114.60       $1,218.7513   $1,218.75   $1,218.75   $1,218.70