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 $62.80   4.610%   $65.6951   $65.70   $65.70   $65.70  
  Purchase #2 $172.96   9.826%   $189.955   $189.96   $189.95   $190.00  
  Purchase #3 $242.33   13.229%   $274.3878   $274.39   $274.40   $274.40  
  Purchase #4 $142.26   7.192%   $152.4913   $152.49   $152.50   $152.50  
  Purchase #5 $158.73   5.167%   $166.9316   $166.93   $166.95   $166.90  
  Purchase #6 $67.34   3.612%   $69.7723   $69.77   $69.75   $69.80  
  Purchase #7 $103.64   3.230%   $106.9876   $106.99   $107.00   $107.00  
  7 purchase totals = $950.06       $1,026.2207   $1,026.23   $1,026.25   $1,026.30