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 $52.49   11.836%   $58.7027   $58.70   $58.70   $58.70  
  Purchase #2 $156.82   11.808%   $175.3373   $175.34   $175.35   $175.30  
  Purchase #3 $167.64   11.779%   $187.3863   $187.39   $187.40   $187.40  
  Purchase #4 $98.52   9.763%   $108.1385   $108.14   $108.15   $108.10  
  Purchase #5 $237.97   6.791%   $254.1305   $254.13   $254.15   $254.10  
  Purchase #6 $71.26   3.573%   $73.8061   $73.81   $73.80   $73.80  
  Purchase #7 $231.90   13.242%   $262.6082   $262.61   $262.60   $262.60  
  7 purchase totals = $1,016.60       $1,120.1096   $1,120.12   $1,120.15   $1,120.00