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 $92.68   11.156%   $103.0194   $103.02   $103.00   $103.00  
  Purchase #2 $248.60   9.797%   $272.9553   $272.96   $272.95   $273.00  
  Purchase #3 $195.94   6.121%   $207.9335   $207.93   $207.95   $207.90  
  Purchase #4 $14.68   5.435%   $15.4779   $15.48   $15.50   $15.50  
  Purchase #5 $34.65   4.404%   $36.176   $36.18   $36.20   $36.20  
  Purchase #6 $143.46   12.291%   $161.0927   $161.09   $161.10   $161.10  
  Purchase #7 $46.44   9.118%   $50.6744   $50.67   $50.65   $50.70  
  7 purchase totals = $776.45       $847.3292   $847.33   $847.35   $847.40