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 $238.45   9.472%   $261.036   $261.04   $261.05   $261.00  
  Purchase #2 $94.79   7.229%   $101.6424   $101.64   $101.65   $101.60  
  Purchase #3 $204.88   8.130%   $221.5367   $221.54   $221.55   $221.50  
  Purchase #4 $187.34   10.822%   $207.6139   $207.61   $207.60   $207.60  
  Purchase #5 $63.40   11.785%   $70.8717   $70.87   $70.85   $70.90  
  Purchase #6 $245.42   11.858%   $274.5219   $274.52   $274.50   $274.50  
  Purchase #7 $213.25   12.826%   $240.6014   $240.60   $240.60   $240.60  
  7 purchase totals = $1,247.53       $1,377.8240   $1,377.82   $1,377.80   $1,377.70