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 $46.95   10.500%   $51.8798   $51.88   $51.90   $51.90  
  Purchase #2 $174.57   4.831%   $183.0035   $183.00   $183.00   $183.00  
  Purchase #3 $152.85   7.626%   $164.5063   $164.51   $164.50   $164.50  
  Purchase #4 $147.28   13.793%   $167.5943   $167.59   $167.60   $167.60  
  Purchase #5 $148.99   5.336%   $156.9401   $156.94   $156.95   $156.90  
  Purchase #6 $134.84   7.585%   $145.0676   $145.07   $145.05   $145.10  
  Purchase #7 $169.54   3.786%   $175.9588   $175.96   $175.95   $176.00  
  7 purchase totals = $975.02       $1,044.9504   $1,044.95   $1,044.95   $1,045.00