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 $76.36   11.118%   $84.8497   $84.85   $84.85   $84.80  
  Purchase #2 $127.65   13.394%   $144.7474   $144.75   $144.75   $144.70  
  Purchase #3 $120.28   4.224%   $125.3606   $125.36   $125.35   $125.40  
  Purchase #4 $162.80   8.380%   $176.4426   $176.44   $176.45   $176.40  
  Purchase #5 $231.72   9.337%   $253.3557   $253.36   $253.35   $253.40  
  Purchase #6 $56.90   12.395%   $63.9528   $63.95   $63.95   $64.00  
  Purchase #7 $161.50   12.382%   $181.4969   $181.50   $181.50   $181.50  
  7 purchase totals = $937.21       $1,030.2057   $1,030.21   $1,030.20   $1,030.20