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 $189.65   12.431%   $213.2254   $213.23   $213.25   $213.20  
  Purchase #2 $182.38   13.483%   $206.9703   $206.97   $206.95   $207.00  
  Purchase #3 $233.54   6.414%   $248.5193   $248.52   $248.50   $248.50  
  Purchase #4 $69.96   3.398%   $72.3372   $72.34   $72.35   $72.30  
  Purchase #5 $120.44   6.715%   $128.5275   $128.53   $128.55   $128.50  
  Purchase #6 $249.64   12.673%   $281.2769   $281.28   $281.30   $281.30  
  Purchase #7 $181.44   12.132%   $203.4523   $203.45   $203.45   $203.50  
  7 purchase totals = $1,227.05       $1,354.3089   $1,354.32   $1,354.35   $1,354.30