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 $181.45   8.414%   $196.7172   $196.72   $196.70   $196.70  
  Purchase #2 $62.58   11.244%   $69.6165   $69.62   $69.60   $69.60  
  Purchase #3 $55.32   7.146%   $59.2732   $59.27   $59.25   $59.30  
  Purchase #4 $183.98   10.366%   $203.0514   $203.05   $203.05   $203.10  
  Purchase #5 $165.41   9.260%   $180.727   $180.73   $180.75   $180.70  
  Purchase #6 $60.33   9.516%   $66.071   $66.07   $66.05   $66.10  
  Purchase #7 $203.92   4.107%   $212.295   $212.30   $212.30   $212.30  
  7 purchase totals = $912.99       $987.7513   $987.76   $987.70   $987.80