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 $89.34   8.473%   $96.9098   $96.91   $96.90   $96.90  
  Purchase #2 $109.93   6.280%   $116.8336   $116.83   $116.85   $116.80  
  Purchase #3 $175.68   3.168%   $181.2455   $181.25   $181.25   $181.20  
  Purchase #4 $100.84   13.244%   $114.1952   $114.20   $114.20   $114.20  
  Purchase #5 $62.26   3.764%   $64.6035   $64.60   $64.60   $64.60  
  Purchase #6 $204.69   9.750%   $224.6473   $224.65   $224.65   $224.60  
  Purchase #7 $208.31   5.166%   $219.0713   $219.07   $219.05   $219.10  
  7 purchase totals = $951.05       $1,017.5062   $1,017.51   $1,017.50   $1,017.40