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 $45.59   7.641%   $49.0735   $49.07   $49.05   $49.10  
  Purchase #2 $249.57   5.514%   $263.3313   $263.33   $263.35   $263.30  
  Purchase #3 $60.55   6.502%   $64.487   $64.49   $64.50   $64.50  
  Purchase #4 $152.60   8.345%   $165.3345   $165.33   $165.35   $165.30  
  Purchase #5 $205.50   12.698%   $231.5944   $231.59   $231.60   $231.60  
  Purchase #6 $120.78   10.622%   $133.6093   $133.61   $133.60   $133.60  
  Purchase #7 $171.71   5.851%   $181.7568   $181.76   $181.75   $181.80  
  7 purchase totals = $1,006.30       $1,089.1868   $1,089.18   $1,089.20   $1,089.20