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 $80.83   6.829%   $86.3499   $86.35   $86.35   $86.30  
  Purchase #2 $96.83   11.518%   $107.9829   $107.98   $108.00   $108.00  
  Purchase #3 $93.56   7.662%   $100.7286   $100.73   $100.75   $100.70  
  Purchase #4 $201.34   9.787%   $221.0451   $221.05   $221.05   $221.00  
  Purchase #5 $29.27   10.432%   $32.3234   $32.32   $32.30   $32.30  
  Purchase #6 $221.81   9.262%   $242.354   $242.35   $242.35   $242.40  
  Purchase #7 $119.70   12.379%   $134.5177   $134.52   $134.50   $134.50  
  7 purchase totals = $843.34       $925.3016   $925.30   $925.30   $925.20