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 $88.25   12.867%   $99.6051   $99.61   $99.60   $99.60  
  Purchase #2 $124.79   4.529%   $130.4417   $130.44   $130.45   $130.40  
  Purchase #3 $112.41   6.571%   $119.7965   $119.80   $119.80   $119.80  
  Purchase #4 $179.74   12.806%   $202.7575   $202.76   $202.75   $202.80  
  Purchase #5 $245.58   4.781%   $257.3212   $257.32   $257.30   $257.30  
  Purchase #6 $38.47   8.748%   $41.8354   $41.84   $41.85   $41.80  
  Purchase #7 $242.64   9.411%   $265.4749   $265.47   $265.45   $265.50  
  7 purchase totals = $1,031.88       $1,117.2323   $1,117.24   $1,117.20   $1,117.20