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 $92.48   5.532%   $97.596   $97.60   $97.60   $97.60  
  Purchase #2 $110.67   12.770%   $124.8026   $124.80   $124.80   $124.80  
  Purchase #3 $246.89   4.577%   $258.1902   $258.19   $258.20   $258.20  
  Purchase #4 $172.97   11.729%   $193.2577   $193.26   $193.25   $193.30  
  Purchase #5 $32.28   7.544%   $34.7152   $34.72   $34.70   $34.70  
  Purchase #6 $229.76   7.682%   $247.4102   $247.41   $247.40   $247.40  
  Purchase #7 $127.84   11.592%   $142.6592   $142.66   $142.65   $142.70  
  7 purchase totals = $1,012.89       $1,098.6311   $1,098.64   $1,098.60   $1,098.70