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 $53.84   9.400%   $58.901   $58.90   $58.90   $58.90  
  Purchase #2 $62.60   5.839%   $66.2552   $66.26   $66.25   $66.30  
  Purchase #3 $142.43   9.437%   $155.8711   $155.87   $155.85   $155.90  
  Purchase #4 $134.41   12.698%   $151.4774   $151.48   $151.50   $151.50  
  Purchase #5 $53.28   4.557%   $55.708   $55.71   $55.70   $55.70  
  Purchase #6 $16.69   5.553%   $17.6168   $17.62   $17.60   $17.60  
  Purchase #7 $203.98   11.249%   $226.9257   $226.93   $226.95   $226.90  
  7 purchase totals = $667.23       $732.7552   $732.77   $732.75   $732.80