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 $93.30   11.174%   $103.7253   $103.73   $103.75   $103.70  
  Purchase #2 $139.53   12.127%   $156.4508   $156.45   $156.45   $156.50  
  Purchase #3 $176.83   12.481%   $198.9002   $198.90   $198.90   $198.90  
  Purchase #4 $105.44   5.184%   $110.906   $110.91   $110.90   $110.90  
  Purchase #5 $151.44   12.809%   $170.8379   $170.84   $170.85   $170.80  
  Purchase #6 $205.33   12.294%   $230.5733   $230.57   $230.55   $230.60  
  Purchase #7 $58.66   8.364%   $63.5663   $63.57   $63.55   $63.60  
  7 purchase totals = $930.53       $1,034.9598   $1,034.97   $1,034.95   $1,035.00