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 $214.65   4.249%   $223.7705   $223.77   $223.75   $223.80  
  Purchase #2 $56.97   13.131%   $64.4507   $64.45   $64.45   $64.50  
  Purchase #3 $132.82   5.103%   $139.5978   $139.60   $139.60   $139.60  
  Purchase #4 $202.70   7.294%   $217.4849   $217.48   $217.50   $217.50  
  Purchase #5 $96.55   10.237%   $106.4338   $106.43   $106.45   $106.40  
  Purchase #6 $31.34   10.221%   $34.5433   $34.54   $34.55   $34.50  
  Purchase #7 $223.86   7.797%   $241.3144   $241.31   $241.30   $241.30  
  7 purchase totals = $958.89       $1,027.5954   $1,027.58   $1,027.60   $1,027.60