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 $57.43   6.113%   $60.9407   $60.94   $60.95   $60.90  
  Purchase #2 $202.27   3.691%   $209.7358   $209.74   $209.75   $209.70  
  Purchase #3 $211.93   10.326%   $233.8139   $233.81   $233.80   $233.80  
  Purchase #4 $32.93   10.813%   $36.4907   $36.49   $36.50   $36.50  
  Purchase #5 $187.59   3.736%   $194.5984   $194.60   $194.60   $194.60  
  Purchase #6 $239.70   11.287%   $266.7549   $266.75   $266.75   $266.80  
  Purchase #7 $129.85   5.168%   $136.5606   $136.56   $136.55   $136.60  
  7 purchase totals = $1,061.70       $1,138.8950   $1,138.89   $1,138.90   $1,138.90