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 $62.83   10.476%   $69.4121   $69.41   $69.40   $69.40  
  Purchase #2 $202.40   11.133%   $224.9332   $224.93   $224.95   $224.90  
  Purchase #3 $225.33   8.381%   $244.2149   $244.21   $244.20   $244.20  
  Purchase #4 $195.96   5.528%   $206.7927   $206.79   $206.80   $206.80  
  Purchase #5 $98.56   11.188%   $109.5869   $109.59   $109.60   $109.60  
  Purchase #6 $31.52   3.699%   $32.6859   $32.69   $32.70   $32.70  
  Purchase #7 $67.85   10.810%   $75.1846   $75.18   $75.20   $75.20  
  7 purchase totals = $884.45       $962.8103   $962.80   $962.85   $962.80