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 $196.49   10.314%   $216.756   $216.76   $216.75   $216.80  
  Purchase #2 $38.45   4.732%   $40.2695   $40.27   $40.25   $40.30  
  Purchase #3 $210.51   10.225%   $232.0346   $232.03   $232.05   $232.00  
  Purchase #4 $246.57   4.783%   $258.3634   $258.36   $258.35   $258.40  
  Purchase #5 $78.31   13.506%   $88.8865   $88.89   $88.90   $88.90  
  Purchase #6 $175.89   9.611%   $192.7948   $192.79   $192.80   $192.80  
  Purchase #7 $211.35   11.270%   $235.1691   $235.17   $235.15   $235.20  
  7 purchase totals = $1,157.57       $1,264.2739   $1,264.27   $1,264.25   $1,264.40