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 $201.50   3.183%   $207.9137   $207.91   $207.90   $207.90  
  Purchase #2 $155.84   4.177%   $162.3494   $162.35   $162.35   $162.30  
  Purchase #3 $233.93   13.103%   $264.5818   $264.58   $264.60   $264.60  
  Purchase #4 $247.93   13.539%   $281.4972   $281.50   $281.50   $281.50  
  Purchase #5 $245.99   12.303%   $276.2541   $276.25   $276.25   $276.30  
  Purchase #6 $244.48   13.352%   $277.123   $277.12   $277.10   $277.10  
  Purchase #7 $245.43   9.573%   $268.925   $268.93   $268.95   $268.90  
  7 purchase totals = $1,575.10       $1,738.6442   $1,738.64   $1,738.65   $1,738.60