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 $216.85   9.390%   $237.2122   $237.21   $237.20   $237.20  
  Purchase #2 $190.26   8.586%   $206.5957   $206.60   $206.60   $206.60  
  Purchase #3 $55.49   5.453%   $58.5159   $58.52   $58.50   $58.50  
  Purchase #4 $56.52   13.628%   $64.2225   $64.22   $64.20   $64.20  
  Purchase #5 $159.32   9.142%   $173.885   $173.89   $173.90   $173.90  
  Purchase #6 $14.71   12.367%   $16.5292   $16.53   $16.55   $16.50  
  Purchase #7 $198.61   13.658%   $225.7362   $225.74   $225.75   $225.70  
  7 purchase totals = $891.76       $982.6967   $982.71   $982.70   $982.60