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 $238.27   12.621%   $268.3421   $268.34   $268.35   $268.30  
  Purchase #2 $140.51   6.559%   $149.7261   $149.73   $149.75   $149.70  
  Purchase #3 $228.67   12.688%   $257.6836   $257.68   $257.70   $257.70  
  Purchase #4 $161.72   10.588%   $178.8429   $178.84   $178.85   $178.80  
  Purchase #5 $158.93   7.460%   $170.7862   $170.79   $170.80   $170.80  
  Purchase #6 $43.35   13.805%   $49.3345   $49.33   $49.35   $49.30  
  Purchase #7 $174.84   6.431%   $186.084   $186.08   $186.10   $186.10  
  7 purchase totals = $1,146.29       $1,260.7994   $1,260.79   $1,260.90   $1,260.70