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 $51.67   9.225%   $56.4366   $56.44   $56.45   $56.40  
  Purchase #2 $232.79   6.775%   $248.5615   $248.56   $248.55   $248.60  
  Purchase #3 $25.43   3.433%   $26.303   $26.30   $26.30   $26.30  
  Purchase #4 $54.37   7.822%   $58.6228   $58.62   $58.60   $58.60  
  Purchase #5 $147.96   5.651%   $156.3212   $156.32   $156.30   $156.30  
  Purchase #6 $137.77   6.184%   $146.2897   $146.29   $146.30   $146.30  
  Purchase #7 $228.60   5.409%   $240.965   $240.97   $240.95   $241.00  
  7 purchase totals = $878.59       $933.4998   $933.50   $933.45   $933.50