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 $177.49   9.178%   $193.78   $193.78   $193.80   $193.80  
  Purchase #2 $246.36   7.815%   $265.613   $265.61   $265.60   $265.60  
  Purchase #3 $167.50   3.849%   $173.9471   $173.95   $173.95   $173.90  
  Purchase #4 $182.46   10.621%   $201.8391   $201.84   $201.85   $201.80  
  Purchase #5 $204.61   5.605%   $216.0784   $216.08   $216.10   $216.10  
  Purchase #6 $111.96   3.585%   $115.9738   $115.97   $115.95   $116.00  
  Purchase #7 $52.91   5.327%   $55.7285   $55.73   $55.75   $55.70  
  7 purchase totals = $1,143.29       $1,222.9599   $1,222.96   $1,223.00   $1,222.90