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 $150.33   11.781%   $168.0404   $168.04   $168.05   $168.00  
  Purchase #2 $235.82   3.828%   $244.8472   $244.85   $244.85   $244.80  
  Purchase #3 $230.80   6.626%   $246.0928   $246.09   $246.10   $246.10  
  Purchase #4 $215.41   6.166%   $228.6922   $228.69   $228.70   $228.70  
  Purchase #5 $53.25   6.701%   $56.8183   $56.82   $56.80   $56.80  
  Purchase #6 $46.53   5.859%   $49.2562   $49.26   $49.25   $49.30  
  Purchase #7 $180.38   9.756%   $197.9779   $197.98   $198.00   $198.00  
  7 purchase totals = $1,112.52       $1,191.7250   $1,191.73   $1,191.75   $1,191.70