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 $164.46   7.157%   $176.2304   $176.23   $176.25   $176.20  
  Purchase #2 $132.27   9.174%   $144.4044   $144.40   $144.40   $144.40  
  Purchase #3 $156.62   13.525%   $177.8029   $177.80   $177.80   $177.80  
  Purchase #4 $83.54   13.688%   $94.975   $94.98   $95.00   $95.00  
  Purchase #5 $28.45   7.620%   $30.6179   $30.62   $30.60   $30.60  
  Purchase #6 $133.97   11.411%   $149.2573   $149.26   $149.25   $149.30  
  Purchase #7 $144.25   9.302%   $157.6681   $157.67   $157.65   $157.70  
  7 purchase totals = $843.56       $930.9560   $930.96   $930.95   $931.00