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 $175.52   5.839%   $185.7686   $185.77   $185.75   $185.80  
  Purchase #2 $88.40   11.185%   $98.2875   $98.29   $98.30   $98.30  
  Purchase #3 $78.99   3.582%   $81.8194   $81.82   $81.80   $81.80  
  Purchase #4 $151.46   9.215%   $165.417   $165.42   $165.40   $165.40  
  Purchase #5 $82.78   6.806%   $88.414   $88.41   $88.40   $88.40  
  Purchase #6 $187.42   12.149%   $210.1897   $210.19   $210.20   $210.20  
  Purchase #7 $23.26   7.492%   $25.0026   $25.00   $25.00   $25.00  
  7 purchase totals = $787.83       $854.8988   $854.90   $854.85   $854.90