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 $188.96   12.758%   $213.0675   $213.07   $213.05   $213.10  
  Purchase #2 $152.71   8.518%   $165.7178   $165.72   $165.70   $165.70  
  Purchase #3 $62.94   7.690%   $67.7801   $67.78   $67.80   $67.80  
  Purchase #4 $124.91   7.702%   $134.5306   $134.53   $134.55   $134.50  
  Purchase #5 $155.90   6.601%   $166.191   $166.19   $166.20   $166.20  
  Purchase #6 $175.86   7.755%   $189.4979   $189.50   $189.50   $189.50  
  Purchase #7 $21.86   12.126%   $24.5107   $24.51   $24.50   $24.50  
  7 purchase totals = $883.14       $961.2956   $961.30   $961.30   $961.30