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 $110.83   13.380%   $125.6591   $125.66   $125.65   $125.70  
  Purchase #2 $152.62   9.842%   $167.6409   $167.64   $167.65   $167.60  
  Purchase #3 $155.95   12.502%   $175.4469   $175.45   $175.45   $175.40  
  Purchase #4 $97.97   12.221%   $109.9429   $109.94   $109.95   $109.90  
  Purchase #5 $41.75   7.207%   $44.7589   $44.76   $44.75   $44.80  
  Purchase #6 $230.68   9.170%   $251.8334   $251.83   $251.85   $251.80  
  Purchase #7 $155.45   11.587%   $173.462   $173.46   $173.45   $173.50  
  7 purchase totals = $945.25       $1,048.7441   $1,048.74   $1,048.75   $1,048.70