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 $63.34   13.524%   $71.9061   $71.91   $71.90   $71.90  
  Purchase #2 $213.62   6.317%   $227.1144   $227.11   $227.10   $227.10  
  Purchase #3 $147.33   13.773%   $167.6218   $167.62   $167.60   $167.60  
  Purchase #4 $47.93   8.236%   $51.8775   $51.88   $51.90   $51.90  
  Purchase #5 $5.26   5.791%   $5.5646   $5.56   $5.55   $5.60  
  Purchase #6 $244.52   9.712%   $268.2678   $268.27   $268.25   $268.30  
  Purchase #7 $135.98   7.741%   $146.5062   $146.51   $146.50   $146.50  
  7 purchase totals = $857.98       $938.8584   $938.86   $938.80   $938.90