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 $223.54   8.202%   $241.8748   $241.87   $241.85   $241.90  
  Purchase #2 $167.45   8.538%   $181.7469   $181.75   $181.75   $181.70  
  Purchase #3 $204.73   13.217%   $231.7892   $231.79   $231.80   $231.80  
  Purchase #4 $24.79   8.592%   $26.92   $26.92   $26.90   $26.90  
  Purchase #5 $56.40   11.637%   $62.9633   $62.96   $62.95   $63.00  
  Purchase #6 $189.80   10.461%   $209.655   $209.66   $209.65   $209.70  
  Purchase #7 $190.60   10.314%   $210.2585   $210.26   $210.25   $210.30  
  7 purchase totals = $1,057.31       $1,165.2077   $1,165.21   $1,165.15   $1,165.30