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 $184.34   13.107%   $208.5014   $208.50   $208.50   $208.50  
  Purchase #2 $63.72   3.521%   $65.9636   $65.96   $65.95   $66.00  
  Purchase #3 $14.45   11.412%   $16.099   $16.10   $16.10   $16.10  
  Purchase #4 $236.86   7.253%   $254.0395   $254.04   $254.05   $254.00  
  Purchase #5 $92.65   11.518%   $103.3214   $103.32   $103.30   $103.30  
  Purchase #6 $29.51   9.190%   $32.222   $32.22   $32.20   $32.20  
  Purchase #7 $178.31   10.400%   $196.8542   $196.85   $196.85   $196.90  
  7 purchase totals = $799.84       $877.0011   $876.99   $876.95   $877.00