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 $68.80   6.580%   $73.327   $73.33   $73.35   $73.30  
  Purchase #2 $9.58   9.409%   $10.4814   $10.48   $10.50   $10.50  
  Purchase #3 $25.39   3.616%   $26.3081   $26.31   $26.30   $26.30  
  Purchase #4 $59.59   5.738%   $63.0093   $63.01   $63.00   $63.00  
  Purchase #5 $41.61   6.472%   $44.303   $44.30   $44.30   $44.30  
  Purchase #6 $33.55   8.855%   $36.5209   $36.52   $36.50   $36.50  
  Purchase #7 $207.85   13.609%   $236.1363   $236.14   $236.15   $236.10  
  7 purchase totals = $446.37       $490.0860   $490.09   $490.10   $490.00