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 $58.71   11.363%   $65.3812   $65.38   $65.40   $65.40  
  Purchase #2 $176.82   4.489%   $184.7574   $184.76   $184.75   $184.80  
  Purchase #3 $132.46   8.353%   $143.5244   $143.52   $143.50   $143.50  
  Purchase #4 $12.30   10.221%   $13.5572   $13.56   $13.55   $13.60  
  Purchase #5 $153.65   13.450%   $174.3159   $174.32   $174.30   $174.30  
  Purchase #6 $56.90   5.182%   $59.8486   $59.85   $59.85   $59.80  
  Purchase #7 $70.26   7.225%   $75.3363   $75.34   $75.35   $75.30  
  7 purchase totals = $661.10       $716.7210   $716.73   $716.70   $716.70