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 $44.74   12.427%   $50.2998   $50.30   $50.30   $50.30  
  Purchase #2 $200.87   8.193%   $217.3273   $217.33   $217.35   $217.30  
  Purchase #3 $33.80   3.246%   $34.8971   $34.90   $34.90   $34.90  
  Purchase #4 $244.58   7.374%   $262.6153   $262.62   $262.60   $262.60  
  Purchase #5 $120.52   11.294%   $134.1315   $134.13   $134.15   $134.10  
  Purchase #6 $111.39   13.678%   $126.6259   $126.63   $126.65   $126.60  
  Purchase #7 $180.75   3.628%   $187.3076   $187.31   $187.30   $187.30  
  7 purchase totals = $936.65       $1,013.2045   $1,013.22   $1,013.25   $1,013.10