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 $111.65   10.402%   $123.2638   $123.26   $123.25   $123.30  
  Purchase #2 $170.46   9.607%   $186.8361   $186.84   $186.85   $186.80  
  Purchase #3 $230.40   3.602%   $238.699   $238.70   $238.70   $238.70  
  Purchase #4 $114.28   6.596%   $121.8179   $121.82   $121.80   $121.80  
  Purchase #5 $181.77   10.208%   $200.3251   $200.33   $200.35   $200.30  
  Purchase #6 $111.48   13.619%   $126.6625   $126.66   $126.65   $126.70  
  Purchase #7 $56.58   7.114%   $60.6051   $60.61   $60.60   $60.60  
  7 purchase totals = $976.62       $1,058.2095   $1,058.22   $1,058.20   $1,058.20