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 $80.82   6.232%   $85.8567   $85.86   $85.85   $85.90  
  Purchase #2 $139.33   6.366%   $148.1997   $148.20   $148.20   $148.20  
  Purchase #3 $207.34   7.616%   $223.131   $223.13   $223.15   $223.10  
  Purchase #4 $92.88   4.805%   $97.3429   $97.34   $97.35   $97.30  
  Purchase #5 $39.49   9.391%   $43.1985   $43.20   $43.20   $43.20  
  Purchase #6 $84.60   6.701%   $90.269   $90.27   $90.25   $90.30  
  Purchase #7 $62.63   10.784%   $69.384   $69.38   $69.40   $69.40  
  7 purchase totals = $707.09       $757.3818   $757.38   $757.40   $757.40