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 $56.32   9.376%   $61.6006   $61.60   $61.60   $61.60  
  Purchase #2 $239.89   8.539%   $260.3742   $260.37   $260.35   $260.40  
  Purchase #3 $21.94   13.754%   $24.9576   $24.96   $24.95   $25.00  
  Purchase #4 $5.26   4.235%   $5.4828   $5.48   $5.50   $5.50  
  Purchase #5 $231.54   3.838%   $240.4265   $240.43   $240.45   $240.40  
  Purchase #6 $169.34   7.826%   $182.5925   $182.59   $182.60   $182.60  
  Purchase #7 $226.29   12.624%   $254.8568   $254.86   $254.85   $254.90  
  7 purchase totals = $950.58       $1,030.2910   $1,030.29   $1,030.30   $1,030.40