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 $84.89   10.623%   $93.9079   $93.91   $93.90   $93.90  
  Purchase #2 $213.99   4.401%   $223.4077   $223.41   $223.40   $223.40  
  Purchase #3 $106.87   3.584%   $110.7002   $110.70   $110.70   $110.70  
  Purchase #4 $217.81   5.512%   $229.8157   $229.82   $229.80   $229.80  
  Purchase #5 $131.66   9.579%   $144.2717   $144.27   $144.25   $144.30  
  Purchase #6 $246.72   3.160%   $254.5164   $254.52   $254.50   $254.50  
  Purchase #7 $5.68   13.487%   $6.4461   $6.45   $6.45   $6.40  
  7 purchase totals = $1,007.62       $1,063.0657   $1,063.08   $1,063.00   $1,063.00