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 $65.93   13.503%   $74.8325   $74.83   $74.85   $74.80  
  Purchase #2 $44.90   7.718%   $48.3654   $48.37   $48.35   $48.40  
  Purchase #3 $13.81   4.167%   $14.3855   $14.39   $14.40   $14.40  
  Purchase #4 $207.95   13.126%   $235.2455   $235.25   $235.25   $235.20  
  Purchase #5 $92.57   7.572%   $99.5794   $99.58   $99.60   $99.60  
  Purchase #6 $126.50   7.619%   $136.138   $136.14   $136.15   $136.10  
  Purchase #7 $59.70   7.206%   $64.002   $64.00   $64.00   $64.00  
  7 purchase totals = $611.36       $672.5483   $672.56   $672.60   $672.50