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 $118.41   10.596%   $130.9567   $130.96   $130.95   $131.00  
  Purchase #2 $127.45   7.379%   $136.8545   $136.85   $136.85   $136.90  
  Purchase #3 $58.78   7.512%   $63.1956   $63.20   $63.20   $63.20  
  Purchase #4 $6.41   7.214%   $6.8724   $6.87   $6.85   $6.90  
  Purchase #5 $228.65   6.507%   $243.5283   $243.53   $243.55   $243.50  
  Purchase #6 $84.97   7.162%   $91.0556   $91.06   $91.05   $91.10  
  Purchase #7 $43.84   5.519%   $46.2595   $46.26   $46.25   $46.30  
  7 purchase totals = $668.51       $718.7226   $718.73   $718.70   $718.90