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 $66.31   11.851%   $74.1684   $74.17   $74.15   $74.20  
  Purchase #2 $23.36   5.258%   $24.5883   $24.59   $24.60   $24.60  
  Purchase #3 $191.89   3.483%   $198.5735   $198.57   $198.55   $198.60  
  Purchase #4 $15.65   7.625%   $16.8433   $16.84   $16.85   $16.80  
  Purchase #5 $213.86   8.797%   $232.6733   $232.67   $232.65   $232.70  
  Purchase #6 $198.36   3.298%   $204.9019   $204.90   $204.90   $204.90  
  Purchase #7 $159.28   9.390%   $174.2364   $174.24   $174.25   $174.20  
  7 purchase totals = $868.71       $925.9851   $925.98   $925.95   $926.00