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 $63.37   13.478%   $71.911   $71.91   $71.90   $71.90  
  Purchase #2 $78.42   3.145%   $80.8863   $80.89   $80.90   $80.90  
  Purchase #3 $84.72   12.358%   $95.1897   $95.19   $95.20   $95.20  
  Purchase #4 $104.77   13.490%   $118.9035   $118.90   $118.90   $118.90  
  Purchase #5 $13.67   7.819%   $14.7389   $14.74   $14.75   $14.70  
  Purchase #6 $244.38   6.341%   $259.8761   $259.88   $259.90   $259.90  
  Purchase #7 $196.65   4.616%   $205.7274   $205.73   $205.75   $205.70  
  7 purchase totals = $785.98       $847.2329   $847.24   $847.30   $847.20