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 $33.25   8.218%   $35.9825   $35.98   $36.00   $36.00  
  Purchase #2 $187.25   6.357%   $199.1535   $199.15   $199.15   $199.20  
  Purchase #3 $23.68   3.351%   $24.4735   $24.47   $24.45   $24.50  
  Purchase #4 $116.44   7.206%   $124.8307   $124.83   $124.85   $124.80  
  Purchase #5 $176.80   8.375%   $191.607   $191.61   $191.60   $191.60  
  Purchase #6 $153.94   7.236%   $165.0791   $165.08   $165.10   $165.10  
  Purchase #7 $69.96   8.500%   $75.9066   $75.91   $75.90   $75.90  
  7 purchase totals = $761.32       $817.0329   $817.03   $817.05   $817.10