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 $92.43   10.702%   $102.3219   $102.32   $102.30   $102.30  
  Purchase #2 $217.80   4.361%   $227.2983   $227.30   $227.30   $227.30  
  Purchase #3 $160.73   12.644%   $181.0527   $181.05   $181.05   $181.10  
  Purchase #4 $84.73   6.325%   $90.0892   $90.09   $90.10   $90.10  
  Purchase #5 $165.94   6.580%   $176.8589   $176.86   $176.85   $176.90  
  Purchase #6 $71.90   12.649%   $80.9946   $80.99   $81.00   $81.00  
  Purchase #7 $78.71   4.140%   $81.9686   $81.97   $81.95   $82.00  
  7 purchase totals = $872.24       $940.5842   $940.58   $940.55   $940.70