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 $82.70   9.474%   $90.535   $90.54   $90.55   $90.50  
  Purchase #2 $237.58   8.199%   $257.0592   $257.06   $257.05   $257.10  
  Purchase #3 $162.36   11.669%   $181.3058   $181.31   $181.30   $181.30  
  Purchase #4 $180.37   4.803%   $189.0332   $189.03   $189.05   $189.00  
  Purchase #5 $235.86   6.388%   $250.9267   $250.93   $250.95   $250.90  
  Purchase #6 $139.62   6.109%   $148.1494   $148.15   $148.15   $148.10  
  Purchase #7 $225.77   11.533%   $251.8081   $251.81   $251.80   $251.80  
  7 purchase totals = $1,264.26       $1,368.8174   $1,368.83   $1,368.85   $1,368.70