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 $52.42   10.615%   $57.9844   $57.98   $58.00   $58.00  
  Purchase #2 $240.29   10.143%   $264.6626   $264.66   $264.65   $264.70  
  Purchase #3 $176.67   8.301%   $191.3354   $191.34   $191.35   $191.30  
  Purchase #4 $80.84   8.575%   $87.772   $87.77   $87.75   $87.80  
  Purchase #5 $194.55   11.348%   $216.6275   $216.63   $216.65   $216.60  
  Purchase #6 $221.54   4.750%   $232.0632   $232.06   $232.05   $232.10  
  Purchase #7 $7.37   11.414%   $8.2112   $8.21   $8.20   $8.20  
  7 purchase totals = $973.68       $1,058.6563   $1,058.65   $1,058.65   $1,058.70