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 $48.42   8.261%   $52.42   $52.42   $52.40   $52.40  
  Purchase #2 $128.74   6.573%   $137.2021   $137.20   $137.20   $137.20  
  Purchase #3 $70.72   13.239%   $80.0826   $80.08   $80.10   $80.10  
  Purchase #4 $147.66   9.598%   $161.8324   $161.83   $161.85   $161.80  
  Purchase #5 $49.95   6.802%   $53.3476   $53.35   $53.35   $53.30  
  Purchase #6 $226.83   11.607%   $253.1582   $253.16   $253.15   $253.20  
  Purchase #7 $235.30   3.697%   $243.999   $244.00   $244.00   $244.00  
  7 purchase totals = $907.62       $982.0419   $982.04   $982.05   $982.00