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 $233.59   13.346%   $264.7649   $264.76   $264.75   $264.80  
  Purchase #2 $197.55   3.865%   $205.1853   $205.19   $205.20   $205.20  
  Purchase #3 $72.82   13.502%   $82.6522   $82.65   $82.65   $82.70  
  Purchase #4 $169.27   7.361%   $181.73   $181.73   $181.75   $181.70  
  Purchase #5 $48.86   8.363%   $52.9462   $52.95   $52.95   $52.90  
  Purchase #6 $157.87   4.750%   $165.3688   $165.37   $165.35   $165.40  
  Purchase #7 $73.76   10.694%   $81.6479   $81.65   $81.65   $81.60  
  7 purchase totals = $953.72       $1,034.2953   $1,034.30   $1,034.30   $1,034.30