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 $243.27   7.127%   $260.6079   $260.61   $260.60   $260.60  
  Purchase #2 $107.72   4.256%   $112.3046   $112.30   $112.30   $112.30  
  Purchase #3 $32.58   11.154%   $36.214   $36.21   $36.20   $36.20  
  Purchase #4 $220.35   3.678%   $228.4545   $228.45   $228.45   $228.50  
  Purchase #5 $79.51   4.422%   $83.0259   $83.03   $83.05   $83.00  
  Purchase #6 $5.99   9.507%   $6.5595   $6.56   $6.55   $6.60  
  Purchase #7 $218.81   8.796%   $238.0565   $238.06   $238.05   $238.10  
  7 purchase totals = $908.23       $965.2229   $965.22   $965.20   $965.30