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 $94.52   8.791%   $102.8293   $102.83   $102.85   $102.80  
  Purchase #2 $30.42   13.173%   $34.4272   $34.43   $34.45   $34.40  
  Purchase #3 $104.98   13.104%   $118.7366   $118.74   $118.75   $118.70  
  Purchase #4 $78.60   4.115%   $81.8344   $81.83   $81.85   $81.80  
  Purchase #5 $151.70   13.372%   $171.9853   $171.99   $172.00   $172.00  
  Purchase #6 $176.49   9.179%   $192.69   $192.69   $192.70   $192.70  
  Purchase #7 $111.34   3.324%   $115.0409   $115.04   $115.05   $115.00  
  7 purchase totals = $748.05       $817.5437   $817.55   $817.65   $817.40