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 $218.50   12.677%   $246.1992   $246.20   $246.20   $246.20  
  Purchase #2 $223.33   13.445%   $253.3567   $253.36   $253.35   $253.40  
  Purchase #3 $155.75   7.291%   $167.1057   $167.11   $167.10   $167.10  
  Purchase #4 $228.82   11.191%   $254.4272   $254.43   $254.45   $254.40  
  Purchase #5 $247.33   9.338%   $270.4257   $270.43   $270.45   $270.40  
  Purchase #6 $82.46   10.329%   $90.9773   $90.98   $91.00   $91.00  
  Purchase #7 $156.40   5.765%   $165.4165   $165.42   $165.40   $165.40  
  7 purchase totals = $1,312.59       $1,447.9083   $1,447.93   $1,447.95   $1,447.90