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 $87.86   8.340%   $95.1875   $95.19   $95.20   $95.20  
  Purchase #2 $94.98   5.751%   $100.4423   $100.44   $100.45   $100.40  
  Purchase #3 $232.77   9.850%   $255.6978   $255.70   $255.70   $255.70  
  Purchase #4 $248.93   6.656%   $265.4988   $265.50   $265.50   $265.50  
  Purchase #5 $95.62   7.287%   $102.5878   $102.59   $102.60   $102.60  
  Purchase #6 $71.65   13.159%   $81.0784   $81.08   $81.10   $81.10  
  Purchase #7 $65.51   13.256%   $74.194   $74.19   $74.20   $74.20  
  7 purchase totals = $897.32       $974.6866   $974.69   $974.75   $974.70