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 $162.59   11.363%   $181.0651   $181.07   $181.05   $181.10  
  Purchase #2 $202.93   9.619%   $222.4498   $222.45   $222.45   $222.40  
  Purchase #3 $51.95   9.251%   $56.7559   $56.76   $56.75   $56.80  
  Purchase #4 $222.70   11.370%   $248.021   $248.02   $248.00   $248.00  
  Purchase #5 $203.61   10.237%   $224.4536   $224.45   $224.45   $224.50  
  Purchase #6 $136.92   13.423%   $155.2988   $155.30   $155.30   $155.30  
  Purchase #7 $248.74   11.549%   $277.467   $277.47   $277.45   $277.50  
  7 purchase totals = $1,229.44       $1,365.5112   $1,365.52   $1,365.45   $1,365.60