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 $211.25   5.425%   $222.7103   $222.71   $222.70   $222.70  
  Purchase #2 $9.86   7.168%   $10.5668   $10.57   $10.55   $10.60  
  Purchase #3 $86.83   5.485%   $91.5926   $91.59   $91.60   $91.60  
  Purchase #4 $23.26   4.401%   $24.2837   $24.28   $24.30   $24.30  
  Purchase #5 $99.82   9.418%   $109.221   $109.22   $109.20   $109.20  
  Purchase #6 $221.57   11.599%   $247.2699   $247.27   $247.25   $247.30  
  Purchase #7 $43.62   12.572%   $49.1039   $49.10   $49.10   $49.10  
  7 purchase totals = $696.21       $754.7482   $754.74   $754.70   $754.80