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 $38.66   11.716%   $43.1894   $43.19   $43.20   $43.20  
  Purchase #2 $167.36   10.640%   $185.1671   $185.17   $185.15   $185.20  
  Purchase #3 $184.29   10.774%   $204.1454   $204.15   $204.15   $204.10  
  Purchase #4 $78.83   12.749%   $88.88   $88.88   $88.90   $88.90  
  Purchase #5 $56.92   9.242%   $62.1805   $62.18   $62.20   $62.20  
  Purchase #6 $220.64   12.416%   $248.0347   $248.03   $248.05   $248.00  
  Purchase #7 $19.94   12.154%   $22.3635   $22.36   $22.35   $22.40  
  7 purchase totals = $766.64       $853.9606   $853.96   $854.00   $854.00