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 $61.41   11.145%   $68.2541   $68.25   $68.25   $68.30  
  Purchase #2 $181.26   4.716%   $189.8082   $189.81   $189.80   $189.80  
  Purchase #3 $98.69   6.112%   $104.7219   $104.72   $104.70   $104.70  
  Purchase #4 $150.43   6.329%   $159.9507   $159.95   $159.95   $160.00  
  Purchase #5 $208.57   4.743%   $218.4625   $218.46   $218.45   $218.50  
  Purchase #6 $185.79   11.114%   $206.4387   $206.44   $206.45   $206.40  
  Purchase #7 $238.69   7.535%   $256.6753   $256.68   $256.70   $256.70  
  7 purchase totals = $1,124.84       $1,204.3114   $1,204.31   $1,204.30   $1,204.40