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 $117.61   9.234%   $128.4701   $128.47   $128.45   $128.50  
  Purchase #2 $112.99   7.624%   $121.6044   $121.60   $121.60   $121.60  
  Purchase #3 $162.67   12.844%   $183.5633   $183.56   $183.55   $183.60  
  Purchase #4 $116.74   11.552%   $130.2258   $130.23   $130.25   $130.20  
  Purchase #5 $134.51   13.809%   $153.0845   $153.08   $153.10   $153.10  
  Purchase #6 $93.65   7.671%   $100.8339   $100.83   $100.85   $100.80  
  Purchase #7 $82.70   11.738%   $92.4073   $92.41   $92.40   $92.40  
  7 purchase totals = $820.87       $910.1893   $910.18   $910.20   $910.20