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 $190.89   12.257%   $214.2874   $214.29   $214.30   $214.30  
  Purchase #2 $60.91   11.580%   $67.9634   $67.96   $67.95   $68.00  
  Purchase #3 $109.88   8.873%   $119.6297   $119.63   $119.65   $119.60  
  Purchase #4 $154.99   5.708%   $163.8368   $163.84   $163.85   $163.80  
  Purchase #5 $61.83   6.638%   $65.9343   $65.93   $65.95   $65.90  
  Purchase #6 $213.31   10.431%   $235.5604   $235.56   $235.55   $235.60  
  Purchase #7 $246.31   10.285%   $271.643   $271.64   $271.65   $271.60  
  7 purchase totals = $1,038.12       $1,138.8550   $1,138.85   $1,138.90   $1,138.80