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 $247.38   8.196%   $267.6553   $267.66   $267.65   $267.70  
  Purchase #2 $192.68   10.344%   $212.6108   $212.61   $212.60   $212.60  
  Purchase #3 $244.94   7.588%   $263.526   $263.53   $263.55   $263.50  
  Purchase #4 $219.93   8.136%   $237.8235   $237.82   $237.80   $237.80  
  Purchase #5 $214.65   13.652%   $243.954   $243.95   $243.95   $244.00  
  Purchase #6 $107.98   5.468%   $113.8843   $113.88   $113.90   $113.90  
  Purchase #7 $26.41   8.341%   $28.6129   $28.61   $28.60   $28.60  
  7 purchase totals = $1,253.97       $1,368.0668   $1,368.06   $1,368.05   $1,368.10