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 $61.68   8.461%   $66.8987   $66.90   $66.90   $66.90  
  Purchase #2 $178.45   4.774%   $186.9692   $186.97   $186.95   $187.00  
  Purchase #3 $56.35   11.399%   $62.7733   $62.77   $62.75   $62.80  
  Purchase #4 $208.39   6.371%   $221.6665   $221.67   $221.65   $221.70  
  Purchase #5 $215.84   3.353%   $223.0771   $223.08   $223.10   $223.10  
  Purchase #6 $120.41   8.287%   $130.3884   $130.39   $130.40   $130.40  
  Purchase #7 $173.26   12.292%   $194.5571   $194.56   $194.55   $194.60  
  7 purchase totals = $1,014.38       $1,086.3303   $1,086.34   $1,086.30   $1,086.50