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 $86.47   12.359%   $97.1568   $97.16   $97.15   $97.20  
  Purchase #2 $23.57   8.312%   $25.5291   $25.53   $25.55   $25.50  
  Purchase #3 $128.57   4.704%   $134.6179   $134.62   $134.60   $134.60  
  Purchase #4 $77.28   13.250%   $87.5196   $87.52   $87.50   $87.50  
  Purchase #5 $142.76   13.251%   $161.6771   $161.68   $161.70   $161.70  
  Purchase #6 $183.65   5.574%   $193.8867   $193.89   $193.90   $193.90  
  Purchase #7 $83.63   11.648%   $93.3712   $93.37   $93.35   $93.40  
  7 purchase totals = $725.93       $793.7584   $793.77   $793.75   $793.80