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 $202.89   12.678%   $228.6124   $228.61   $228.60   $228.60  
  Purchase #2 $243.55   5.733%   $257.5127   $257.51   $257.50   $257.50  
  Purchase #3 $162.53   9.431%   $177.8582   $177.86   $177.85   $177.90  
  Purchase #4 $53.88   12.567%   $60.6511   $60.65   $60.65   $60.70  
  Purchase #5 $216.75   6.778%   $231.4413   $231.44   $231.45   $231.40  
  Purchase #6 $42.61   3.370%   $44.046   $44.05   $44.05   $44.00  
  Purchase #7 $162.54   7.254%   $174.3307   $174.33   $174.35   $174.30  
  7 purchase totals = $1,084.75       $1,174.4524   $1,174.45   $1,174.45   $1,174.40