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 $21.62   6.455%   $23.0156   $23.02   $23.00   $23.00  
  Purchase #2 $150.30   11.325%   $167.3215   $167.32   $167.30   $167.30  
  Purchase #3 $201.45   10.546%   $222.6949   $222.69   $222.70   $222.70  
  Purchase #4 $86.54   7.530%   $93.0565   $93.06   $93.05   $93.10  
  Purchase #5 $248.77   8.115%   $268.9577   $268.96   $268.95   $269.00  
  Purchase #6 $226.98   11.515%   $253.1167   $253.12   $253.10   $253.10  
  Purchase #7 $59.37   13.739%   $67.5268   $67.53   $67.55   $67.50  
  7 purchase totals = $995.03       $1,095.6897   $1,095.70   $1,095.65   $1,095.70