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 $52.33   9.775%   $57.4453   $57.45   $57.45   $57.40  
  Purchase #2 $134.83   10.759%   $149.3364   $149.34   $149.35   $149.30  
  Purchase #3 $160.32   9.445%   $175.4622   $175.46   $175.45   $175.50  
  Purchase #4 $101.93   8.285%   $110.3749   $110.37   $110.35   $110.40  
  Purchase #5 $131.74   4.547%   $137.7302   $137.73   $137.75   $137.70  
  Purchase #6 $207.58   4.636%   $217.2034   $217.20   $217.20   $217.20  
  Purchase #7 $209.50   7.367%   $224.9339   $224.93   $224.95   $224.90  
  7 purchase totals = $998.23       $1,072.4863   $1,072.48   $1,072.50   $1,072.40