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 $53.96   5.747%   $57.0611   $57.06   $57.05   $57.10  
  Purchase #2 $25.45   13.855%   $28.9761   $28.98   $29.00   $29.00  
  Purchase #3 $6.83   10.666%   $7.5585   $7.56   $7.55   $7.60  
  Purchase #4 $127.75   8.648%   $138.7978   $138.80   $138.80   $138.80  
  Purchase #5 $21.45   6.334%   $22.8086   $22.81   $22.80   $22.80  
  Purchase #6 $139.75   7.456%   $150.1698   $150.17   $150.15   $150.20  
  Purchase #7 $39.91   6.812%   $42.6287   $42.63   $42.65   $42.60  
  7 purchase totals = $415.10       $448.0006   $448.01   $448.00   $448.10