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 $211.63   11.799%   $236.6002   $236.60   $236.60   $236.60  
  Purchase #2 $143.31   9.423%   $156.8141   $156.81   $156.80   $156.80  
  Purchase #3 $226.79   11.374%   $252.5851   $252.59   $252.60   $252.60  
  Purchase #4 $209.49   4.131%   $218.144   $218.14   $218.15   $218.10  
  Purchase #5 $120.95   6.563%   $128.8879   $128.89   $128.90   $128.90  
  Purchase #6 $58.82   12.139%   $65.9602   $65.96   $65.95   $66.00  
  Purchase #7 $210.65   3.140%   $217.2644   $217.26   $217.25   $217.30  
  7 purchase totals = $1,181.64       $1,276.2559   $1,276.25   $1,276.25   $1,276.30