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 $231.84   12.558%   $260.9545   $260.95   $260.95   $261.00  
  Purchase #2 $158.71   6.536%   $169.0833   $169.08   $169.10   $169.10  
  Purchase #3 $60.31   5.241%   $63.4708   $63.47   $63.45   $63.50  
  Purchase #4 $71.52   5.290%   $75.3034   $75.30   $75.30   $75.30  
  Purchase #5 $11.80   3.478%   $12.2104   $12.21   $12.20   $12.20  
  Purchase #6 $250.89   12.626%   $282.5674   $282.57   $282.55   $282.60  
  Purchase #7 $231.36   10.252%   $255.079   $255.08   $255.10   $255.10  
  7 purchase totals = $1,016.43       $1,118.6688   $1,118.66   $1,118.65   $1,118.80