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 $58.55   7.637%   $63.0215   $63.02   $63.00   $63.00  
  Purchase #2 $184.90   5.441%   $194.9604   $194.96   $194.95   $195.00  
  Purchase #3 $241.73   11.508%   $269.5483   $269.55   $269.55   $269.50  
  Purchase #4 $155.58   6.213%   $165.2462   $165.25   $165.25   $165.20  
  Purchase #5 $108.42   9.680%   $118.9151   $118.92   $118.90   $118.90  
  Purchase #6 $116.66   3.585%   $120.8423   $120.84   $120.85   $120.80  
  Purchase #7 $59.87   7.738%   $64.5027   $64.50   $64.50   $64.50  
  7 purchase totals = $925.71       $997.0365   $997.04   $997.00   $996.90