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 $61.53   12.860%   $69.4428   $69.44   $69.45   $69.40  
  Purchase #2 $241.82   7.648%   $260.3144   $260.31   $260.30   $260.30  
  Purchase #3 $119.86   4.295%   $125.008   $125.01   $125.00   $125.00  
  Purchase #4 $68.86   5.844%   $72.8842   $72.88   $72.90   $72.90  
  Purchase #5 $97.31   7.744%   $104.8457   $104.85   $104.85   $104.80  
  Purchase #6 $217.94   5.652%   $230.258   $230.26   $230.25   $230.30  
  Purchase #7 $216.94   8.539%   $235.4645   $235.46   $235.45   $235.50  
  7 purchase totals = $1,024.26       $1,098.2176   $1,098.21   $1,098.20   $1,098.20