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 $65.60   4.363%   $68.4621   $68.46   $68.45   $68.50  
  Purchase #2 $97.46   8.804%   $106.0404   $106.04   $106.05   $106.00  
  Purchase #3 $207.67   12.106%   $232.8105   $232.81   $232.80   $232.80  
  Purchase #4 $133.57   8.819%   $145.3495   $145.35   $145.35   $145.30  
  Purchase #5 $249.91   13.842%   $284.5025   $284.50   $284.50   $284.50  
  Purchase #6 $6.25   9.195%   $6.8247   $6.82   $6.80   $6.80  
  Purchase #7 $199.72   8.145%   $215.9872   $215.99   $216.00   $216.00  
  7 purchase totals = $960.18       $1,059.9769   $1,059.97   $1,059.95   $1,059.90