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 $66.82   7.620%   $71.9117   $71.91   $71.90   $71.90  
  Purchase #2 $49.55   9.157%   $54.0873   $54.09   $54.10   $54.10  
  Purchase #3 $114.26   10.474%   $126.2276   $126.23   $126.25   $126.20  
  Purchase #4 $244.65   10.554%   $270.4704   $270.47   $270.45   $270.50  
  Purchase #5 $207.78   10.742%   $230.0997   $230.10   $230.10   $230.10  
  Purchase #6 $236.79   13.270%   $268.212   $268.21   $268.20   $268.20  
  Purchase #7 $72.53   4.358%   $75.6909   $75.69   $75.70   $75.70  
  7 purchase totals = $992.38       $1,096.6996   $1,096.70   $1,096.70   $1,096.70