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 $144.52   7.559%   $155.4443   $155.44   $155.45   $155.40  
  Purchase #2 $147.39   10.115%   $162.2985   $162.30   $162.30   $162.30  
  Purchase #3 $240.99   12.661%   $271.5017   $271.50   $271.50   $271.50  
  Purchase #4 $145.27   7.359%   $155.9604   $155.96   $155.95   $156.00  
  Purchase #5 $247.67   5.412%   $261.0739   $261.07   $261.05   $261.10  
  Purchase #6 $11.60   4.625%   $12.1365   $12.14   $12.15   $12.10  
  Purchase #7 $25.57   3.458%   $26.4542   $26.45   $26.45   $26.50  
  7 purchase totals = $963.01       $1,044.8695   $1,044.86   $1,044.85   $1,044.90