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 $53.89   13.285%   $61.0493   $61.05   $61.05   $61.00  
  Purchase #2 $184.99   11.780%   $206.7818   $206.78   $206.80   $206.80  
  Purchase #3 $138.60   12.281%   $155.6215   $155.62   $155.60   $155.60  
  Purchase #4 $174.29   8.320%   $188.7909   $188.79   $188.80   $188.80  
  Purchase #5 $247.94   7.437%   $266.3793   $266.38   $266.40   $266.40  
  Purchase #6 $85.64   9.626%   $93.8837   $93.88   $93.90   $93.90  
  Purchase #7 $188.90   6.589%   $201.3466   $201.35   $201.35   $201.30  
  7 purchase totals = $1,074.25       $1,173.8531   $1,173.85   $1,173.90   $1,173.80