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 $200.38   6.202%   $212.8076   $212.81   $212.80   $212.80  
  Purchase #2 $231.99   4.115%   $241.5364   $241.54   $241.55   $241.50  
  Purchase #3 $10.27   11.609%   $11.4622   $11.46   $11.45   $11.50  
  Purchase #4 $81.71   3.667%   $84.7063   $84.71   $84.70   $84.70  
  Purchase #5 $174.67   4.148%   $181.9153   $181.92   $181.90   $181.90  
  Purchase #6 $65.89   3.131%   $67.953   $67.95   $67.95   $68.00  
  Purchase #7 $206.45   7.830%   $222.615   $222.62   $222.60   $222.60  
  7 purchase totals = $971.36       $1,022.9958   $1,023.01   $1,022.95   $1,023.00