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 $92.27   4.758%   $96.6602   $96.66   $96.65   $96.70  
  Purchase #2 $77.48   3.395%   $80.1104   $80.11   $80.10   $80.10  
  Purchase #3 $217.83   6.268%   $231.4836   $231.48   $231.50   $231.50  
  Purchase #4 $165.90   8.575%   $180.1259   $180.13   $180.15   $180.10  
  Purchase #5 $116.34   7.642%   $125.2307   $125.23   $125.25   $125.20  
  Purchase #6 $159.43   12.103%   $178.7258   $178.73   $178.75   $178.70  
  Purchase #7 $128.95   4.162%   $134.3169   $134.32   $134.30   $134.30  
  7 purchase totals = $958.20       $1,026.6535   $1,026.66   $1,026.70   $1,026.60