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 $173.82   13.834%   $197.8663   $197.87   $197.85   $197.90  
  Purchase #2 $118.29   8.713%   $128.5966   $128.60   $128.60   $128.60  
  Purchase #3 $79.29   11.358%   $88.2958   $88.30   $88.30   $88.30  
  Purchase #4 $127.51   5.236%   $134.1864   $134.19   $134.20   $134.20  
  Purchase #5 $202.44   10.584%   $223.8662   $223.87   $223.85   $223.90  
  Purchase #6 $236.56   13.149%   $267.6653   $267.67   $267.65   $267.70  
  Purchase #7 $59.62   10.316%   $65.7704   $65.77   $65.75   $65.80  
  7 purchase totals = $997.53       $1,106.2470   $1,106.27   $1,106.20   $1,106.40