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 $66.94   10.192%   $73.7625   $73.76   $73.75   $73.80  
  Purchase #2 $60.51   12.687%   $68.1869   $68.19   $68.20   $68.20  
  Purchase #3 $216.26   11.216%   $240.5157   $240.52   $240.50   $240.50  
  Purchase #4 $24.66   3.225%   $25.4553   $25.46   $25.45   $25.50  
  Purchase #5 $25.47   5.346%   $26.8316   $26.83   $26.85   $26.80  
  Purchase #6 $172.98   6.651%   $184.4849   $184.48   $184.50   $184.50  
  Purchase #7 $139.75   10.639%   $154.618   $154.62   $154.60   $154.60  
  7 purchase totals = $706.57       $773.8549   $773.86   $773.85   $773.90