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 $34.83   6.116%   $36.9602   $36.96   $36.95   $37.00  
  Purchase #2 $192.66   10.529%   $212.9452   $212.95   $212.95   $212.90  
  Purchase #3 $98.28   13.133%   $111.1871   $111.19   $111.20   $111.20  
  Purchase #4 $202.99   7.558%   $218.332   $218.33   $218.35   $218.30  
  Purchase #5 $97.35   5.116%   $102.3304   $102.33   $102.35   $102.30  
  Purchase #6 $72.91   12.198%   $81.8036   $81.80   $81.80   $81.80  
  Purchase #7 $207.25   6.432%   $220.5803   $220.58   $220.60   $220.60  
  7 purchase totals = $906.27       $984.1388   $984.14   $984.20   $984.10