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 $153.41   5.266%   $161.4886   $161.49   $161.50   $161.50  
  Purchase #2 $134.54   9.686%   $147.5715   $147.57   $147.55   $147.60  
  Purchase #3 $26.25   13.613%   $29.8234   $29.82   $29.80   $29.80  
  Purchase #4 $116.86   6.572%   $124.54   $124.54   $124.55   $124.50  
  Purchase #5 $93.55   10.107%   $103.0051   $103.01   $103.00   $103.00  
  Purchase #6 $84.52   11.189%   $93.9769   $93.98   $94.00   $94.00  
  Purchase #7 $115.25   7.241%   $123.5953   $123.60   $123.60   $123.60  
  7 purchase totals = $724.38       $784.0008   $784.01   $784.00   $784.00