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 $228.56   13.470%   $259.347   $259.35   $259.35   $259.30  
  Purchase #2 $207.57   12.629%   $233.784   $233.78   $233.80   $233.80  
  Purchase #3 $79.79   6.294%   $84.812   $84.81   $84.80   $84.80  
  Purchase #4 $46.64   11.139%   $51.8352   $51.84   $51.85   $51.80  
  Purchase #5 $238.27   11.703%   $266.1547   $266.15   $266.15   $266.20  
  Purchase #6 $39.60   13.862%   $45.0894   $45.09   $45.10   $45.10  
  Purchase #7 $135.41   5.750%   $143.1961   $143.20   $143.20   $143.20  
  7 purchase totals = $975.84       $1,084.2184   $1,084.22   $1,084.25   $1,084.20