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 $114.53   3.257%   $118.2602   $118.26   $118.25   $118.30  
  Purchase #2 $187.41   13.341%   $212.4124   $212.41   $212.40   $212.40  
  Purchase #3 $96.94   10.605%   $107.2205   $107.22   $107.20   $107.20  
  Purchase #4 $121.90   10.386%   $134.5605   $134.56   $134.55   $134.60  
  Purchase #5 $223.32   13.317%   $253.0595   $253.06   $253.05   $253.10  
  Purchase #6 $82.98   5.549%   $87.5846   $87.58   $87.60   $87.60  
  Purchase #7 $80.84   7.664%   $87.0356   $87.04   $87.05   $87.00  
  7 purchase totals = $907.92       $1,000.1333   $1,000.13   $1,000.10   $1,000.20