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 $68.63   7.229%   $73.5913   $73.59   $73.60   $73.60  
  Purchase #2 $249.43   10.585%   $275.8322   $275.83   $275.85   $275.80  
  Purchase #3 $154.65   13.372%   $175.3298   $175.33   $175.35   $175.30  
  Purchase #4 $7.75   12.130%   $8.6901   $8.69   $8.70   $8.70  
  Purchase #5 $103.84   5.469%   $109.519   $109.52   $109.50   $109.50  
  Purchase #6 $175.90   5.150%   $184.9589   $184.96   $184.95   $185.00  
  Purchase #7 $110.56   4.596%   $115.6413   $115.64   $115.65   $115.60  
  7 purchase totals = $870.76       $943.5626   $943.56   $943.60   $943.50