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 $197.50   8.515%   $214.3171   $214.32   $214.30   $214.30  
  Purchase #2 $215.76   8.298%   $233.6638   $233.66   $233.65   $233.70  
  Purchase #3 $30.73   6.662%   $32.7772   $32.78   $32.80   $32.80  
  Purchase #4 $136.93   8.788%   $148.9634   $148.96   $148.95   $149.00  
  Purchase #5 $99.85   3.170%   $103.0152   $103.02   $103.00   $103.00  
  Purchase #6 $200.66   6.179%   $213.0588   $213.06   $213.05   $213.10  
  Purchase #7 $49.52   13.763%   $56.3354   $56.34   $56.35   $56.30  
  7 purchase totals = $930.95       $1,002.1309   $1,002.14   $1,002.10   $1,002.20