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 $186.75   4.282%   $194.7466   $194.75   $194.75   $194.70  
  Purchase #2 $218.49   8.517%   $237.0988   $237.10   $237.10   $237.10  
  Purchase #3 $227.33   10.315%   $250.7791   $250.78   $250.80   $250.80  
  Purchase #4 $173.59   13.827%   $197.5923   $197.59   $197.60   $197.60  
  Purchase #5 $233.73   8.110%   $252.6855   $252.69   $252.70   $252.70  
  Purchase #6 $68.50   13.381%   $77.666   $77.67   $77.65   $77.70  
  Purchase #7 $163.58   13.842%   $186.2227   $186.22   $186.20   $186.20  
  7 purchase totals = $1,271.97       $1,396.7910   $1,396.80   $1,396.80   $1,396.80