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 $240.96   7.564%   $259.1862   $259.19   $259.20   $259.20  
  Purchase #2 $152.37   5.323%   $160.4807   $160.48   $160.50   $160.50  
  Purchase #3 $140.49   7.296%   $150.7402   $150.74   $150.75   $150.70  
  Purchase #4 $175.39   7.396%   $188.3618   $188.36   $188.35   $188.40  
  Purchase #5 $93.58   3.279%   $96.6485   $96.65   $96.65   $96.60  
  Purchase #6 $95.39   5.230%   $100.3789   $100.38   $100.40   $100.40  
  Purchase #7 $226.95   11.169%   $252.298   $252.30   $252.30   $252.30  
  7 purchase totals = $1,125.13       $1,208.0943   $1,208.10   $1,208.15   $1,208.10