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 $69.80   4.516%   $72.9522   $72.95   $72.95   $73.00  
  Purchase #2 $178.40   8.379%   $193.3481   $193.35   $193.35   $193.30  
  Purchase #3 $233.50   12.239%   $262.0781   $262.08   $262.10   $262.10  
  Purchase #4 $68.50   4.477%   $71.5667   $71.57   $71.55   $71.60  
  Purchase #5 $91.26   6.224%   $96.94   $96.94   $96.95   $96.90  
  Purchase #6 $173.95   12.140%   $195.0675   $195.07   $195.05   $195.10  
  Purchase #7 $141.56   5.484%   $149.3232   $149.32   $149.30   $149.30  
  7 purchase totals = $956.97       $1,041.2758   $1,041.28   $1,041.25   $1,041.30