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 $53.54   12.500%   $60.2325   $60.23   $60.25   $60.20  
  Purchase #2 $94.73   8.847%   $103.1108   $103.11   $103.10   $103.10  
  Purchase #3 $160.51   3.285%   $165.7828   $165.78   $165.80   $165.80  
  Purchase #4 $115.97   9.603%   $127.1066   $127.11   $127.10   $127.10  
  Purchase #5 $216.80   10.782%   $240.1754   $240.18   $240.20   $240.20  
  Purchase #6 $45.96   3.619%   $47.6233   $47.62   $47.60   $47.60  
  Purchase #7 $129.82   6.442%   $138.183   $138.18   $138.20   $138.20  
  7 purchase totals = $817.33       $882.2144   $882.21   $882.25   $882.20