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 $151.89   7.319%   $163.0068   $163.01   $163.00   $163.00  
  Purchase #2 $238.37   10.562%   $263.5466   $263.55   $263.55   $263.50  
  Purchase #3 $193.50   7.154%   $207.343   $207.34   $207.35   $207.30  
  Purchase #4 $198.83   9.767%   $218.2497   $218.25   $218.25   $218.20  
  Purchase #5 $91.28   4.799%   $95.6605   $95.66   $95.65   $95.70  
  Purchase #6 $75.27   13.819%   $85.6716   $85.67   $85.65   $85.70  
  Purchase #7 $35.94   6.422%   $38.2481   $38.25   $38.25   $38.20  
  7 purchase totals = $985.08       $1,071.7263   $1,071.73   $1,071.70   $1,071.60