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 $186.98   3.167%   $192.9017   $192.90   $192.90   $192.90  
  Purchase #2 $13.48   8.502%   $14.6261   $14.63   $14.65   $14.60  
  Purchase #3 $187.37   9.222%   $204.6493   $204.65   $204.65   $204.60  
  Purchase #4 $243.89   3.494%   $252.4115   $252.41   $252.40   $252.40  
  Purchase #5 $62.30   3.845%   $64.6954   $64.70   $64.70   $64.70  
  Purchase #6 $200.53   6.679%   $213.9234   $213.92   $213.90   $213.90  
  Purchase #7 $30.30   9.374%   $33.1403   $33.14   $33.15   $33.10  
  7 purchase totals = $924.85       $976.3477   $976.35   $976.35   $976.20