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 $89.84   9.179%   $98.0864   $98.09   $98.10   $98.10  
  Purchase #2 $215.84   11.278%   $240.1824   $240.18   $240.20   $240.20  
  Purchase #3 $107.85   9.780%   $118.3977   $118.40   $118.40   $118.40  
  Purchase #4 $84.39   4.331%   $88.0449   $88.04   $88.05   $88.00  
  Purchase #5 $247.66   11.806%   $276.8987   $276.90   $276.90   $276.90  
  Purchase #6 $90.43   5.494%   $95.3982   $95.40   $95.40   $95.40  
  Purchase #7 $228.99   8.701%   $248.9144   $248.91   $248.90   $248.90  
  7 purchase totals = $1,065.00       $1,165.9227   $1,165.92   $1,165.95   $1,165.90