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 $221.92   10.833%   $245.9606   $245.96   $245.95   $246.00  
  Purchase #2 $65.83   7.224%   $70.5856   $70.59   $70.60   $70.60  
  Purchase #3 $249.44   9.133%   $272.2214   $272.22   $272.20   $272.20  
  Purchase #4 $242.83   11.231%   $270.1022   $270.10   $270.10   $270.10  
  Purchase #5 $161.51   9.658%   $177.1086   $177.11   $177.10   $177.10  
  Purchase #6 $26.64   7.152%   $28.5453   $28.55   $28.55   $28.50  
  Purchase #7 $188.86   13.309%   $213.9954   $214.00   $214.00   $214.00  
  7 purchase totals = $1,157.03       $1,278.5191   $1,278.53   $1,278.50   $1,278.50