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 $232.92   13.601%   $264.5994   $264.60   $264.60   $264.60  
  Purchase #2 $173.49   6.659%   $185.0427   $185.04   $185.05   $185.00  
  Purchase #3 $91.38   5.589%   $96.4872   $96.49   $96.50   $96.50  
  Purchase #4 $48.85   9.391%   $53.4375   $53.44   $53.45   $53.40  
  Purchase #5 $209.48   6.869%   $223.8692   $223.87   $223.85   $223.90  
  Purchase #6 $165.70   9.531%   $181.4929   $181.49   $181.50   $181.50  
  Purchase #7 $202.43   8.547%   $219.7317   $219.73   $219.75   $219.70  
  7 purchase totals = $1,124.25       $1,224.6606   $1,224.66   $1,224.70   $1,224.60