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 $183.72   6.593%   $195.8327   $195.83   $195.85   $195.80  
  Purchase #2 $39.73   5.844%   $42.0518   $42.05   $42.05   $42.10  
  Purchase #3 $107.40   11.584%   $119.8412   $119.84   $119.85   $119.80  
  Purchase #4 $240.51   6.628%   $256.451   $256.45   $256.45   $256.50  
  Purchase #5 $173.40   11.790%   $193.8439   $193.84   $193.85   $193.80  
  Purchase #6 $34.57   6.693%   $36.8838   $36.88   $36.90   $36.90  
  Purchase #7 $183.91   3.634%   $190.5933   $190.59   $190.60   $190.60  
  7 purchase totals = $963.24       $1,035.4977   $1,035.48   $1,035.55   $1,035.50