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 $55.52   12.331%   $62.3662   $62.37   $62.35   $62.40  
  Purchase #2 $232.55   5.186%   $244.61   $244.61   $244.60   $244.60  
  Purchase #3 $171.61   12.866%   $193.6893   $193.69   $193.70   $193.70  
  Purchase #4 $234.39   11.673%   $261.7503   $261.75   $261.75   $261.80  
  Purchase #5 $33.76   7.144%   $36.1718   $36.17   $36.15   $36.20  
  Purchase #6 $120.87   9.308%   $132.1206   $132.12   $132.10   $132.10  
  Purchase #7 $12.66   10.255%   $13.9583   $13.96   $13.95   $14.00  
  7 purchase totals = $861.36       $944.6665   $944.67   $944.60   $944.80