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 $231.55   13.838%   $263.5919   $263.59   $263.60   $263.60  
  Purchase #2 $184.90   3.593%   $191.5435   $191.54   $191.55   $191.50  
  Purchase #3 $152.39   11.369%   $169.7152   $169.72   $169.70   $169.70  
  Purchase #4 $173.96   12.673%   $196.006   $196.01   $196.00   $196.00  
  Purchase #5 $144.94   4.273%   $151.1333   $151.13   $151.15   $151.10  
  Purchase #6 $21.44   8.180%   $23.1938   $23.19   $23.20   $23.20  
  Purchase #7 $210.64   8.764%   $229.1005   $229.10   $229.10   $229.10  
  7 purchase totals = $1,119.82       $1,224.2842   $1,224.28   $1,224.30   $1,224.20