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 $186.59   8.860%   $203.1219   $203.12   $203.10   $203.10  
  Purchase #2 $29.67   13.178%   $33.5799   $33.58   $33.60   $33.60  
  Purchase #3 $131.91   8.697%   $143.3822   $143.38   $143.40   $143.40  
  Purchase #4 $76.85   6.648%   $81.959   $81.96   $81.95   $82.00  
  Purchase #5 $153.31   5.613%   $161.9153   $161.92   $161.90   $161.90  
  Purchase #6 $207.54   6.213%   $220.4345   $220.43   $220.45   $220.40  
  Purchase #7 $169.39   4.494%   $177.0024   $177.00   $177.00   $177.00  
  7 purchase totals = $955.26       $1,021.3952   $1,021.39   $1,021.40   $1,021.40