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 $57.96   9.133%   $63.2535   $63.25   $63.25   $63.30  
  Purchase #2 $34.67   8.369%   $37.5715   $37.57   $37.55   $37.60  
  Purchase #3 $110.47   3.226%   $114.0338   $114.03   $114.05   $114.00  
  Purchase #4 $40.65   12.600%   $45.7719   $45.77   $45.75   $45.80  
  Purchase #5 $6.40   10.137%   $7.0488   $7.05   $7.05   $7.00  
  Purchase #6 $176.59   13.810%   $200.9771   $200.98   $201.00   $201.00  
  Purchase #7 $229.49   3.667%   $237.9054   $237.91   $237.90   $237.90  
  7 purchase totals = $656.23       $706.5620   $706.56   $706.55   $706.60