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 $97.57   7.204%   $104.5989   $104.60   $104.60   $104.60  
  Purchase #2 $6.67   4.404%   $6.9637   $6.96   $6.95   $7.00  
  Purchase #3 $65.38   12.668%   $73.6623   $73.66   $73.65   $73.70  
  Purchase #4 $16.46   6.703%   $17.5633   $17.56   $17.55   $17.60  
  Purchase #5 $211.68   3.850%   $219.8297   $219.83   $219.85   $219.80  
  Purchase #6 $172.82   6.285%   $183.6817   $183.68   $183.70   $183.70  
  Purchase #7 $232.87   7.351%   $249.9883   $249.99   $250.00   $250.00  
  7 purchase totals = $803.45       $856.2879   $856.28   $856.30   $856.40