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 $88.92   4.200%   $92.6546   $92.65   $92.65   $92.70  
  Purchase #2 $162.42   3.793%   $168.5806   $168.58   $168.60   $168.60  
  Purchase #3 $194.57   6.780%   $207.7618   $207.76   $207.75   $207.80  
  Purchase #4 $170.59   3.717%   $176.9308   $176.93   $176.95   $176.90  
  Purchase #5 $99.97   3.286%   $103.255   $103.26   $103.25   $103.30  
  Purchase #6 $95.43   9.412%   $104.4119   $104.41   $104.40   $104.40  
  Purchase #7 $24.79   7.394%   $26.623   $26.62   $26.60   $26.60  
  7 purchase totals = $836.69       $880.2177   $880.21   $880.20   $880.30