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 $171.54   12.644%   $193.2295   $193.23   $193.25   $193.20  
  Purchase #2 $193.53   11.527%   $215.8382   $215.84   $215.85   $215.80  
  Purchase #3 $112.74   7.787%   $121.5191   $121.52   $121.50   $121.50  
  Purchase #4 $180.49   8.568%   $195.9544   $195.95   $195.95   $196.00  
  Purchase #5 $196.59   5.253%   $206.9169   $206.92   $206.90   $206.90  
  Purchase #6 $57.39   9.182%   $62.6595   $62.66   $62.65   $62.70  
  Purchase #7 $217.48   12.610%   $244.9042   $244.90   $244.90   $244.90  
  7 purchase totals = $1,129.76       $1,241.0218   $1,241.02   $1,241.00   $1,241.00