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 $198.27   13.364%   $224.7668   $224.77   $224.75   $224.80  
  Purchase #2 $207.97   8.458%   $225.5601   $225.56   $225.55   $225.60  
  Purchase #3 $38.43   7.199%   $41.1966   $41.20   $41.20   $41.20  
  Purchase #4 $119.78   6.554%   $127.6304   $127.63   $127.65   $127.60  
  Purchase #5 $198.29   6.155%   $210.4947   $210.49   $210.50   $210.50  
  Purchase #6 $72.72   10.397%   $80.2807   $80.28   $80.30   $80.30  
  Purchase #7 $134.26   3.270%   $138.6503   $138.65   $138.65   $138.70  
  7 purchase totals = $969.72       $1,048.5796   $1,048.58   $1,048.60   $1,048.70