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 $213.96   7.587%   $230.1931   $230.19   $230.20   $230.20  
  Purchase #2 $217.33   4.283%   $226.6382   $226.64   $226.65   $226.60  
  Purchase #3 $22.61   8.714%   $24.5802   $24.58   $24.60   $24.60  
  Purchase #4 $234.97   4.343%   $245.1747   $245.17   $245.15   $245.20  
  Purchase #5 $74.69   3.185%   $77.0689   $77.07   $77.05   $77.10  
  Purchase #6 $74.95   7.290%   $80.4139   $80.41   $80.40   $80.40  
  Purchase #7 $42.64   10.469%   $47.104   $47.10   $47.10   $47.10  
  7 purchase totals = $881.15       $931.1730   $931.16   $931.15   $931.20