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 $216.38   13.107%   $244.7409   $244.74   $244.75   $244.70  
  Purchase #2 $184.87   9.197%   $201.8725   $201.87   $201.85   $201.90  
  Purchase #3 $207.46   8.834%   $225.787   $225.79   $225.80   $225.80  
  Purchase #4 $46.58   3.524%   $48.2215   $48.22   $48.20   $48.20  
  Purchase #5 $196.94   13.253%   $223.0405   $223.04   $223.05   $223.00  
  Purchase #6 $107.50   9.871%   $118.1113   $118.11   $118.10   $118.10  
  Purchase #7 $26.32   13.253%   $29.8082   $29.81   $29.80   $29.80  
  7 purchase totals = $986.05       $1,091.5819   $1,091.58   $1,091.55   $1,091.50