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 $43.93   6.604%   $46.8311   $46.83   $46.85   $46.80  
  Purchase #2 $207.54   13.244%   $235.0266   $235.03   $235.05   $235.00  
  Purchase #3 $73.75   9.542%   $80.7872   $80.79   $80.80   $80.80  
  Purchase #4 $211.27   12.203%   $237.0513   $237.05   $237.05   $237.10  
  Purchase #5 $152.64   9.575%   $167.2553   $167.26   $167.25   $167.30  
  Purchase #6 $203.27   13.161%   $230.0224   $230.02   $230.00   $230.00  
  Purchase #7 $34.64   10.510%   $38.2807   $38.28   $38.30   $38.30  
  7 purchase totals = $927.04       $1,035.2546   $1,035.26   $1,035.30   $1,035.30