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 $186.49   8.474%   $202.2932   $202.29   $202.30   $202.30  
  Purchase #2 $108.40   9.542%   $118.7435   $118.74   $118.75   $118.70  
  Purchase #3 $78.79   3.476%   $81.5287   $81.53   $81.55   $81.50  
  Purchase #4 $160.86   6.810%   $171.8146   $171.81   $171.80   $171.80  
  Purchase #5 $193.90   7.125%   $207.7154   $207.72   $207.70   $207.70  
  Purchase #6 $165.44   4.867%   $173.492   $173.49   $173.50   $173.50  
  Purchase #7 $63.69   11.339%   $70.9118   $70.91   $70.90   $70.90  
  7 purchase totals = $957.57       $1,026.4992   $1,026.49   $1,026.50   $1,026.40