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 $190.97   7.174%   $204.6702   $204.67   $204.65   $204.70  
  Purchase #2 $150.68   13.286%   $170.6993   $170.70   $170.70   $170.70  
  Purchase #3 $173.76   4.474%   $181.534   $181.53   $181.55   $181.50  
  Purchase #4 $179.28   12.400%   $201.5107   $201.51   $201.50   $201.50  
  Purchase #5 $60.85   7.231%   $65.2501   $65.25   $65.25   $65.30  
  Purchase #6 $165.28   10.189%   $182.1204   $182.12   $182.10   $182.10  
  Purchase #7 $134.81   12.744%   $151.9902   $151.99   $152.00   $152.00  
  7 purchase totals = $1,055.63       $1,157.7749   $1,157.77   $1,157.75   $1,157.80