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 $92.36   7.502%   $99.2888   $99.29   $99.30   $99.30  
  Purchase #2 $202.38   4.754%   $212.0011   $212.00   $212.00   $212.00  
  Purchase #3 $242.88   5.673%   $256.6586   $256.66   $256.65   $256.70  
  Purchase #4 $198.55   8.206%   $214.843   $214.84   $214.85   $214.80  
  Purchase #5 $120.42   5.673%   $127.2514   $127.25   $127.25   $127.30  
  Purchase #6 $27.99   10.222%   $30.8511   $30.85   $30.85   $30.90  
  Purchase #7 $108.48   9.124%   $118.3777   $118.38   $118.40   $118.40  
  7 purchase totals = $993.06       $1,059.2717   $1,059.27   $1,059.30   $1,059.40