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 $59.52   6.831%   $63.5858   $63.59   $63.60   $63.60  
  Purchase #2 $215.25   7.524%   $231.4454   $231.45   $231.45   $231.40  
  Purchase #3 $238.41   6.707%   $254.4002   $254.40   $254.40   $254.40  
  Purchase #4 $103.63   7.108%   $110.996   $111.00   $111.00   $111.00  
  Purchase #5 $20.52   3.872%   $21.3145   $21.31   $21.30   $21.30  
  Purchase #6 $30.36   12.211%   $34.0673   $34.07   $34.05   $34.10  
  Purchase #7 $30.55   4.106%   $31.8044   $31.80   $31.80   $31.80  
  7 purchase totals = $698.24       $747.6136   $747.62   $747.60   $747.60