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 $196.79   8.104%   $212.7379   $212.74   $212.75   $212.70  
  Purchase #2 $173.65   12.627%   $195.5768   $195.58   $195.60   $195.60  
  Purchase #3 $212.37   9.658%   $232.8807   $232.88   $232.90   $232.90  
  Purchase #4 $242.75   10.442%   $268.098   $268.10   $268.10   $268.10  
  Purchase #5 $226.74   6.676%   $241.8772   $241.88   $241.90   $241.90  
  Purchase #6 $191.51   5.781%   $202.5812   $202.58   $202.60   $202.60  
  Purchase #7 $35.29   12.865%   $39.8301   $39.83   $39.85   $39.80  
  7 purchase totals = $1,279.10       $1,393.5819   $1,393.59   $1,393.70   $1,393.60