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 $115.51   8.515%   $125.3457   $125.35   $125.35   $125.30  
  Purchase #2 $61.34   10.780%   $67.9525   $67.95   $67.95   $68.00  
  Purchase #3 $80.95   6.572%   $86.27   $86.27   $86.25   $86.30  
  Purchase #4 $25.63   4.377%   $26.7518   $26.75   $26.75   $26.80  
  Purchase #5 $224.28   13.507%   $254.5735   $254.57   $254.55   $254.60  
  Purchase #6 $188.81   12.160%   $211.7693   $211.77   $211.75   $211.80  
  Purchase #7 $217.96   11.807%   $243.6945   $243.69   $243.70   $243.70  
  7 purchase totals = $914.48       $1,016.3573   $1,016.35   $1,016.30   $1,016.50