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 $219.42   7.221%   $235.2643   $235.26   $235.25   $235.30  
  Purchase #2 $219.57   3.303%   $226.8224   $226.82   $226.80   $226.80  
  Purchase #3 $32.97   3.309%   $34.061   $34.06   $34.05   $34.10  
  Purchase #4 $249.90   9.629%   $273.9629   $273.96   $273.95   $274.00  
  Purchase #5 $96.89   5.540%   $102.2577   $102.26   $102.25   $102.30  
  Purchase #6 $148.35   3.102%   $152.9518   $152.95   $152.95   $153.00  
  Purchase #7 $126.37   5.170%   $132.9033   $132.90   $132.90   $132.90  
  7 purchase totals = $1,093.47       $1,158.2234   $1,158.21   $1,158.15   $1,158.40