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 $216.98   11.507%   $241.9479   $241.95   $241.95   $241.90  
  Purchase #2 $115.48   9.529%   $126.4841   $126.48   $126.50   $126.50  
  Purchase #3 $135.60   6.435%   $144.3259   $144.33   $144.35   $144.30  
  Purchase #4 $107.58   12.565%   $121.0974   $121.10   $121.10   $121.10  
  Purchase #5 $235.81   4.433%   $246.2635   $246.26   $246.25   $246.30  
  Purchase #6 $34.36   11.163%   $38.1956   $38.20   $38.20   $38.20  
  Purchase #7 $128.60   9.151%   $140.3682   $140.37   $140.35   $140.40  
  7 purchase totals = $974.41       $1,058.6826   $1,058.69   $1,058.70   $1,058.70