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 $95.59   7.451%   $102.7124   $102.71   $102.70   $102.70  
  Purchase #2 $211.71   11.713%   $236.5076   $236.51   $236.50   $236.50  
  Purchase #3 $90.52   7.111%   $96.9569   $96.96   $96.95   $97.00  
  Purchase #4 $223.76   10.866%   $248.0738   $248.07   $248.05   $248.10  
  Purchase #5 $197.96   4.842%   $207.5452   $207.55   $207.55   $207.50  
  Purchase #6 $147.38   9.446%   $161.3015   $161.30   $161.30   $161.30  
  Purchase #7 $81.97   12.729%   $92.404   $92.40   $92.40   $92.40  
  7 purchase totals = $1,048.89       $1,145.5014   $1,145.50   $1,145.45   $1,145.50