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 $201.41   7.689%   $216.8964   $216.90   $216.90   $216.90  
  Purchase #2 $113.53   4.377%   $118.4992   $118.50   $118.50   $118.50  
  Purchase #3 $165.60   8.171%   $179.1312   $179.13   $179.15   $179.10  
  Purchase #4 $154.61   3.304%   $159.7183   $159.72   $159.70   $159.70  
  Purchase #5 $58.25   8.431%   $63.1611   $63.16   $63.15   $63.20  
  Purchase #6 $63.91   4.522%   $66.8   $66.80   $66.80   $66.80  
  Purchase #7 $116.68   3.672%   $120.9645   $120.96   $120.95   $121.00  
  7 purchase totals = $873.99       $925.1707   $925.17   $925.15   $925.20