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 $37.51   9.321%   $41.0063   $41.01   $41.00   $41.00  
  Purchase #2 $195.44   8.372%   $211.8022   $211.80   $211.80   $211.80  
  Purchase #3 $71.84   4.836%   $75.3142   $75.31   $75.30   $75.30  
  Purchase #4 $232.31   7.122%   $248.8551   $248.86   $248.85   $248.90  
  Purchase #5 $192.87   11.751%   $215.5342   $215.53   $215.55   $215.50  
  Purchase #6 $113.89   9.365%   $124.5558   $124.56   $124.55   $124.60  
  Purchase #7 $82.83   9.500%   $90.6989   $90.70   $90.70   $90.70  
  7 purchase totals = $926.69       $1,007.7667   $1,007.77   $1,007.75   $1,007.80