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 $241.36   5.618%   $254.9196   $254.92   $254.90   $254.90  
  Purchase #2 $238.26   8.122%   $257.6115   $257.61   $257.60   $257.60  
  Purchase #3 $26.27   9.206%   $28.6884   $28.69   $28.70   $28.70  
  Purchase #4 $94.64   8.811%   $102.9787   $102.98   $103.00   $103.00  
  Purchase #5 $19.53   11.524%   $21.7806   $21.78   $21.80   $21.80  
  Purchase #6 $152.80   11.604%   $170.5309   $170.53   $170.55   $170.50  
  Purchase #7 $62.67   7.572%   $67.4154   $67.42   $67.40   $67.40  
  7 purchase totals = $835.53       $903.9251   $903.93   $903.95   $903.90