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 $227.93   8.106%   $246.406   $246.41   $246.40   $246.40  
  Purchase #2 $83.67   13.835%   $95.2457   $95.25   $95.25   $95.20  
  Purchase #3 $181.73   9.181%   $198.4146   $198.41   $198.40   $198.40  
  Purchase #4 $179.91   12.257%   $201.9616   $201.96   $201.95   $202.00  
  Purchase #5 $46.57   4.314%   $48.579   $48.58   $48.60   $48.60  
  Purchase #6 $102.89   9.840%   $113.0144   $113.01   $113.00   $113.00  
  Purchase #7 $50.46   12.166%   $56.599   $56.60   $56.60   $56.60  
  7 purchase totals = $873.16       $960.2203   $960.22   $960.20   $960.20