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 $172.28   11.163%   $191.5116   $191.51   $191.50   $191.50  
  Purchase #2 $72.49   6.157%   $76.9532   $76.95   $76.95   $77.00  
  Purchase #3 $52.47   8.152%   $56.7474   $56.75   $56.75   $56.70  
  Purchase #4 $220.67   9.592%   $241.8367   $241.84   $241.85   $241.80  
  Purchase #5 $205.62   9.631%   $225.4233   $225.42   $225.40   $225.40  
  Purchase #6 $209.41   7.815%   $225.7754   $225.78   $225.80   $225.80  
  Purchase #7 $53.35   9.667%   $58.5073   $58.51   $58.50   $58.50  
  7 purchase totals = $986.29       $1,076.7549   $1,076.76   $1,076.75   $1,076.70