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 $61.76   3.331%   $63.8172   $63.82   $63.80   $63.80  
  Purchase #2 $131.29   11.794%   $146.7743   $146.77   $146.75   $146.80  
  Purchase #3 $83.78   8.652%   $91.0286   $91.03   $91.05   $91.00  
  Purchase #4 $160.92   6.340%   $171.1223   $171.12   $171.10   $171.10  
  Purchase #5 $194.55   4.220%   $202.76   $202.76   $202.75   $202.80  
  Purchase #6 $242.46   11.645%   $270.6945   $270.69   $270.70   $270.70  
  Purchase #7 $54.66   10.835%   $60.5824   $60.58   $60.60   $60.60  
  7 purchase totals = $929.42       $1,006.7793   $1,006.77   $1,006.75   $1,006.80