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 $207.99   12.495%   $233.9784   $233.98   $234.00   $234.00  
  Purchase #2 $231.64   3.149%   $238.9343   $238.93   $238.95   $238.90  
  Purchase #3 $214.37   6.304%   $227.8839   $227.88   $227.90   $227.90  
  Purchase #4 $126.82   3.853%   $131.7064   $131.71   $131.70   $131.70  
  Purchase #5 $71.95   12.201%   $80.7286   $80.73   $80.75   $80.70  
  Purchase #6 $55.58   10.790%   $61.5771   $61.58   $61.60   $61.60  
  Purchase #7 $51.84   13.146%   $58.6549   $58.65   $58.65   $58.70  
  7 purchase totals = $960.19       $1,033.4636   $1,033.46   $1,033.55   $1,033.50