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 $62.28   10.693%   $68.9396   $68.94   $68.95   $68.90  
  Purchase #2 $136.62   5.764%   $144.4948   $144.49   $144.50   $144.50  
  Purchase #3 $45.78   13.571%   $51.9928   $51.99   $52.00   $52.00  
  Purchase #4 $225.77   7.410%   $242.4996   $242.50   $242.50   $242.50  
  Purchase #5 $223.61   4.172%   $232.939   $232.94   $232.95   $232.90  
  Purchase #6 $95.78   11.145%   $106.4547   $106.45   $106.45   $106.50  
  Purchase #7 $166.94   9.530%   $182.8494   $182.85   $182.85   $182.80  
  7 purchase totals = $956.78       $1,030.1699   $1,030.16   $1,030.20   $1,030.10