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 $96.89   6.255%   $102.9505   $102.95   $102.95   $103.00  
  Purchase #2 $202.61   6.682%   $216.1484   $216.15   $216.15   $216.10  
  Purchase #3 $25.97   9.557%   $28.452   $28.45   $28.45   $28.50  
  Purchase #4 $49.84   4.797%   $52.2308   $52.23   $52.25   $52.20  
  Purchase #5 $239.77   11.561%   $267.4898   $267.49   $267.50   $267.50  
  Purchase #6 $19.86   12.635%   $22.3693   $22.37   $22.35   $22.40  
  Purchase #7 $178.67   11.106%   $198.5131   $198.51   $198.50   $198.50  
  7 purchase totals = $813.61       $888.1539   $888.15   $888.15   $888.20