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 $65.33   4.444%   $68.2333   $68.23   $68.25   $68.20  
  Purchase #2 $156.81   11.352%   $174.6111   $174.61   $174.60   $174.60  
  Purchase #3 $187.50   10.460%   $207.1125   $207.11   $207.10   $207.10  
  Purchase #4 $77.35   8.301%   $83.7708   $83.77   $83.75   $83.80  
  Purchase #5 $230.44   9.654%   $252.6867   $252.69   $252.70   $252.70  
  Purchase #6 $172.69   12.730%   $194.6734   $194.67   $194.65   $194.70  
  Purchase #7 $107.98   12.752%   $121.7496   $121.75   $121.75   $121.70  
  7 purchase totals = $998.10       $1,102.8374   $1,102.83   $1,102.80   $1,102.80