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 $147.65   6.786%   $157.6695   $157.67   $157.65   $157.70  
  Purchase #2 $116.63   6.591%   $124.3171   $124.32   $124.30   $124.30  
  Purchase #3 $23.37   11.301%   $26.011   $26.01   $26.00   $26.00  
  Purchase #4 $237.39   10.765%   $262.945   $262.95   $262.95   $262.90  
  Purchase #5 $195.69   12.729%   $220.5994   $220.60   $220.60   $220.60  
  Purchase #6 $212.56   6.526%   $226.4317   $226.43   $226.45   $226.40  
  Purchase #7 $19.38   6.164%   $20.5746   $20.57   $20.55   $20.60  
  7 purchase totals = $952.67       $1,038.5483   $1,038.55   $1,038.50   $1,038.50