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 $61.54   12.369%   $69.1519   $69.15   $69.15   $69.20  
  Purchase #2 $67.91   3.563%   $70.3296   $70.33   $70.35   $70.30  
  Purchase #3 $233.85   11.145%   $259.9126   $259.91   $259.90   $259.90  
  Purchase #4 $188.99   11.262%   $210.2741   $210.27   $210.25   $210.30  
  Purchase #5 $14.86   7.811%   $16.0207   $16.02   $16.00   $16.00  
  Purchase #6 $152.76   13.691%   $173.6744   $173.67   $173.65   $173.70  
  Purchase #7 $223.89   12.430%   $251.7195   $251.72   $251.70   $251.70  
  7 purchase totals = $943.80       $1,051.0828   $1,051.07   $1,051.00   $1,051.10