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 $69.87   7.552%   $75.1466   $75.15   $75.15   $75.10  
  Purchase #2 $219.42   8.239%   $237.498   $237.50   $237.50   $237.50  
  Purchase #3 $24.48   5.300%   $25.7774   $25.78   $25.80   $25.80  
  Purchase #4 $8.48   13.584%   $9.6319   $9.63   $9.65   $9.60  
  Purchase #5 $163.85   6.336%   $174.2315   $174.23   $174.25   $174.20  
  Purchase #6 $237.55   10.157%   $261.678   $261.68   $261.70   $261.70  
  Purchase #7 $13.93   4.437%   $14.5481   $14.55   $14.55   $14.50  
  7 purchase totals = $737.58       $798.5115   $798.52   $798.60   $798.40