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 $219.86   12.612%   $247.5887   $247.59   $247.60   $247.60  
  Purchase #2 $145.78   4.827%   $152.8168   $152.82   $152.80   $152.80  
  Purchase #3 $117.46   4.149%   $122.3334   $122.33   $122.35   $122.30  
  Purchase #4 $140.51   4.620%   $147.0016   $147.00   $147.00   $147.00  
  Purchase #5 $102.29   4.825%   $107.2255   $107.23   $107.25   $107.20  
  Purchase #6 $109.56   8.264%   $118.614   $118.61   $118.60   $118.60  
  Purchase #7 $137.77   7.274%   $147.7914   $147.79   $147.80   $147.80  
  7 purchase totals = $973.23       $1,043.3714   $1,043.37   $1,043.40   $1,043.30