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 $74.27   3.142%   $76.6036   $76.60   $76.60   $76.60  
  Purchase #2 $85.84   6.774%   $91.6548   $91.65   $91.65   $91.70  
  Purchase #3 $162.25   6.664%   $173.0623   $173.06   $173.05   $173.10  
  Purchase #4 $42.38   3.641%   $43.9231   $43.92   $43.90   $43.90  
  Purchase #5 $233.89   4.308%   $243.966   $243.97   $243.95   $244.00  
  Purchase #6 $191.30   12.281%   $214.7936   $214.79   $214.80   $214.80  
  Purchase #7 $79.36   5.250%   $83.5264   $83.53   $83.55   $83.50  
  7 purchase totals = $869.29       $927.5298   $927.52   $927.50   $927.60