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 $246.37   3.229%   $254.3253   $254.33   $254.35   $254.30  
  Purchase #2 $83.41   12.122%   $93.521   $93.52   $93.50   $93.50  
  Purchase #3 $147.58   13.644%   $167.7158   $167.72   $167.70   $167.70  
  Purchase #4 $195.25   7.592%   $210.0734   $210.07   $210.05   $210.10  
  Purchase #5 $10.58   9.691%   $11.6053   $11.61   $11.60   $11.60  
  Purchase #6 $54.47   11.373%   $60.6649   $60.66   $60.65   $60.70  
  Purchase #7 $214.54   5.658%   $226.6787   $226.68   $226.70   $226.70  
  7 purchase totals = $952.20       $1,024.5844   $1,024.59   $1,024.55   $1,024.60