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 $146.98   7.702%   $158.3004   $158.30   $158.30   $158.30  
  Purchase #2 $188.28   4.295%   $196.3666   $196.37   $196.35   $196.40  
  Purchase #3 $60.72   7.178%   $65.0785   $65.08   $65.10   $65.10  
  Purchase #4 $134.90   13.499%   $153.1102   $153.11   $153.10   $153.10  
  Purchase #5 $125.39   7.784%   $135.1504   $135.15   $135.15   $135.20  
  Purchase #6 $77.29   9.316%   $84.4903   $84.49   $84.50   $84.50  
  Purchase #7 $115.33   10.201%   $127.0948   $127.09   $127.10   $127.10  
  7 purchase totals = $848.89       $919.5912   $919.59   $919.60   $919.70