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 $188.41   9.728%   $206.7385   $206.74   $206.75   $206.70  
  Purchase #2 $242.95   8.742%   $264.1887   $264.19   $264.20   $264.20  
  Purchase #3 $165.60   8.829%   $180.2208   $180.22   $180.20   $180.20  
  Purchase #4 $232.70   3.416%   $240.649   $240.65   $240.65   $240.60  
  Purchase #5 $89.36   5.772%   $94.5179   $94.52   $94.50   $94.50  
  Purchase #6 $48.33   5.473%   $50.9751   $50.98   $51.00   $51.00  
  Purchase #7 $157.58   6.491%   $167.8085   $167.81   $167.80   $167.80  
  7 purchase totals = $1,124.93       $1,205.0985   $1,205.11   $1,205.10   $1,205.00