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 $99.51   7.478%   $106.9514   $106.95   $106.95   $107.00  
  Purchase #2 $29.41   7.226%   $31.5352   $31.54   $31.55   $31.50  
  Purchase #3 $152.74   6.243%   $162.2756   $162.28   $162.30   $162.30  
  Purchase #4 $152.27   5.167%   $160.1378   $160.14   $160.15   $160.10  
  Purchase #5 $212.67   9.695%   $233.2884   $233.29   $233.30   $233.30  
  Purchase #6 $41.55   9.321%   $45.4229   $45.42   $45.40   $45.40  
  Purchase #7 $60.86   10.159%   $67.0428   $67.04   $67.05   $67.00  
  7 purchase totals = $749.01       $806.6541   $806.66   $806.70   $806.60