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 $187.41   8.275%   $202.9182   $202.92   $202.90   $202.90  
  Purchase #2 $230.95   13.408%   $261.9158   $261.92   $261.90   $261.90  
  Purchase #3 $137.64   11.594%   $153.598   $153.60   $153.60   $153.60  
  Purchase #4 $98.36   4.375%   $102.6633   $102.66   $102.65   $102.70  
  Purchase #5 $56.83   13.795%   $64.6697   $64.67   $64.65   $64.70  
  Purchase #6 $22.92   6.664%   $24.4474   $24.45   $24.45   $24.40  
  Purchase #7 $177.47   8.504%   $192.562   $192.56   $192.55   $192.60  
  7 purchase totals = $911.58       $1,002.7744   $1,002.78   $1,002.70   $1,002.80