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 $151.93   3.781%   $157.6745   $157.67   $157.65   $157.70  
  Purchase #2 $26.84   4.630%   $28.0827   $28.08   $28.10   $28.10  
  Purchase #3 $223.85   10.617%   $247.6162   $247.62   $247.60   $247.60  
  Purchase #4 $69.37   8.500%   $75.2665   $75.27   $75.25   $75.30  
  Purchase #5 $192.88   4.515%   $201.5885   $201.59   $201.60   $201.60  
  Purchase #6 $33.67   13.545%   $38.2306   $38.23   $38.25   $38.20  
  Purchase #7 $233.93   12.533%   $263.2484   $263.25   $263.25   $263.20  
  7 purchase totals = $932.47       $1,011.7074   $1,011.71   $1,011.70   $1,011.70