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 $119.72   6.691%   $127.7305   $127.73   $127.75   $127.70  
  Purchase #2 $83.76   5.866%   $88.6734   $88.67   $88.65   $88.70  
  Purchase #3 $197.85   5.642%   $209.0127   $209.01   $209.00   $209.00  
  Purchase #4 $6.38   7.657%   $6.8685   $6.87   $6.85   $6.90  
  Purchase #5 $176.96   6.271%   $188.0572   $188.06   $188.05   $188.10  
  Purchase #6 $171.36   13.700%   $194.8363   $194.84   $194.85   $194.80  
  Purchase #7 $148.55   7.566%   $159.7893   $159.79   $159.80   $159.80  
  7 purchase totals = $904.58       $974.9679   $974.97   $974.95   $975.00