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 $117.45   5.771%   $124.228   $124.23   $124.25   $124.20  
  Purchase #2 $94.47   9.183%   $103.1452   $103.15   $103.15   $103.10  
  Purchase #3 $36.75   3.761%   $38.1322   $38.13   $38.15   $38.10  
  Purchase #4 $120.27   11.666%   $134.3007   $134.30   $134.30   $134.30  
  Purchase #5 $73.60   7.693%   $79.262   $79.26   $79.25   $79.30  
  Purchase #6 $111.77   5.699%   $118.1398   $118.14   $118.15   $118.10  
  Purchase #7 $192.32   6.117%   $204.0842   $204.08   $204.10   $204.10  
  7 purchase totals = $746.63       $801.2921   $801.29   $801.35   $801.20