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 $65.61   13.656%   $74.5697   $74.57   $74.55   $74.60  
  Purchase #2 $54.34   3.572%   $56.281   $56.28   $56.30   $56.30  
  Purchase #3 $21.95   9.145%   $23.9573   $23.96   $23.95   $24.00  
  Purchase #4 $40.64   11.531%   $45.3262   $45.33   $45.35   $45.30  
  Purchase #5 $162.25   13.797%   $184.6356   $184.64   $184.65   $184.60  
  Purchase #6 $111.93   6.299%   $118.9805   $118.98   $119.00   $119.00  
  Purchase #7 $212.83   9.428%   $232.8956   $232.90   $232.90   $232.90  
  7 purchase totals = $669.55       $736.6459   $736.66   $736.70   $736.70