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 $246.48   10.329%   $271.9389   $271.94   $271.95   $271.90  
  Purchase #2 $193.75   12.294%   $217.5696   $217.57   $217.55   $217.60  
  Purchase #3 $97.60   6.468%   $103.9128   $103.91   $103.90   $103.90  
  Purchase #4 $230.46   11.767%   $257.5782   $257.58   $257.60   $257.60  
  Purchase #5 $156.74   5.846%   $165.903   $165.90   $165.90   $165.90  
  Purchase #6 $165.59   5.466%   $174.6411   $174.64   $174.65   $174.60  
  Purchase #7 $149.98   10.563%   $165.8224   $165.82   $165.80   $165.80  
  7 purchase totals = $1,240.60       $1,357.3660   $1,357.36   $1,357.35   $1,357.30