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 $56.72   3.492%   $58.7007   $58.70   $58.70   $58.70  
  Purchase #2 $166.31   6.545%   $177.195   $177.20   $177.20   $177.20  
  Purchase #3 $131.70   8.482%   $142.8708   $142.87   $142.85   $142.90  
  Purchase #4 $81.72   11.795%   $91.3589   $91.36   $91.35   $91.40  
  Purchase #5 $103.55   3.248%   $106.9133   $106.91   $106.90   $106.90  
  Purchase #6 $245.68   6.193%   $260.895   $260.90   $260.90   $260.90  
  Purchase #7 $186.61   7.461%   $200.533   $200.53   $200.55   $200.50  
  7 purchase totals = $972.29       $1,038.4667   $1,038.47   $1,038.45   $1,038.50