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 $59.76   3.482%   $61.8408   $61.84   $61.85   $61.80  
  Purchase #2 $83.77   11.251%   $93.195   $93.20   $93.20   $93.20  
  Purchase #3 $157.94   7.453%   $169.7113   $169.71   $169.70   $169.70  
  Purchase #4 $127.92   13.142%   $144.7312   $144.73   $144.75   $144.70  
  Purchase #5 $14.52   4.738%   $15.208   $15.21   $15.20   $15.20  
  Purchase #6 $233.44   3.603%   $241.8508   $241.85   $241.85   $241.90  
  Purchase #7 $186.49   13.752%   $212.1361   $212.14   $212.15   $212.10  
  7 purchase totals = $863.84       $938.6732   $938.68   $938.70   $938.60