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 $200.48   8.733%   $217.9879   $217.99   $218.00   $218.00  
  Purchase #2 $153.41   11.482%   $171.0245   $171.02   $171.00   $171.00  
  Purchase #3 $211.56   3.562%   $219.0958   $219.10   $219.10   $219.10  
  Purchase #4 $214.88   4.126%   $223.7459   $223.75   $223.75   $223.70  
  Purchase #5 $60.89   7.798%   $65.6382   $65.64   $65.65   $65.60  
  Purchase #6 $155.39   11.617%   $173.4417   $173.44   $173.45   $173.40  
  Purchase #7 $80.38   3.237%   $82.9819   $82.98   $83.00   $83.00  
  7 purchase totals = $1,076.99       $1,153.9159   $1,153.92   $1,153.95   $1,153.80