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 $61.25   4.566%   $64.0467   $64.05   $64.05   $64.00  
  Purchase #2 $177.83   10.411%   $196.3439   $196.34   $196.35   $196.30  
  Purchase #3 $19.47   9.728%   $21.364   $21.36   $21.35   $21.40  
  Purchase #4 $183.42   11.740%   $204.9535   $204.95   $204.95   $205.00  
  Purchase #5 $199.84   12.470%   $224.76   $224.76   $224.75   $224.80  
  Purchase #6 $114.87   8.418%   $124.5398   $124.54   $124.55   $124.50  
  Purchase #7 $164.42   10.355%   $181.4457   $181.45   $181.45   $181.40  
  7 purchase totals = $921.10       $1,017.4536   $1,017.45   $1,017.45   $1,017.40