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 $54.52   7.302%   $58.5011   $58.50   $58.50   $58.50  
  Purchase #2 $240.98   12.740%   $271.6809   $271.68   $271.70   $271.70  
  Purchase #3 $91.57   4.346%   $95.5496   $95.55   $95.55   $95.50  
  Purchase #4 $166.57   5.433%   $175.6197   $175.62   $175.60   $175.60  
  Purchase #5 $82.99   12.152%   $93.0749   $93.07   $93.05   $93.10  
  Purchase #6 $60.44   10.814%   $66.976   $66.98   $67.00   $67.00  
  Purchase #7 $145.76   9.154%   $159.1029   $159.10   $159.10   $159.10  
  7 purchase totals = $842.83       $920.5051   $920.50   $920.50   $920.50