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 $24.69   7.781%   $26.6111   $26.61   $26.60   $26.60  
  Purchase #2 $140.25   6.489%   $149.3508   $149.35   $149.35   $149.40  
  Purchase #3 $204.51   3.574%   $211.8192   $211.82   $211.80   $211.80  
  Purchase #4 $222.94   9.342%   $243.7671   $243.77   $243.75   $243.80  
  Purchase #5 $143.47   13.358%   $162.6347   $162.63   $162.65   $162.60  
  Purchase #6 $86.82   10.286%   $95.7503   $95.75   $95.75   $95.80  
  Purchase #7 $80.43   6.369%   $85.5526   $85.55   $85.55   $85.60  
  7 purchase totals = $903.11       $975.4858   $975.48   $975.45   $975.60