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 $58.52   9.681%   $64.1853   $64.19   $64.20   $64.20  
  Purchase #2 $164.93   6.588%   $175.7956   $175.80   $175.80   $175.80  
  Purchase #3 $206.98   10.519%   $228.7522   $228.75   $228.75   $228.80  
  Purchase #4 $80.74   13.309%   $91.4857   $91.49   $91.50   $91.50  
  Purchase #5 $235.76   9.865%   $259.0177   $259.02   $259.00   $259.00  
  Purchase #6 $137.89   9.615%   $151.1481   $151.15   $151.15   $151.10  
  Purchase #7 $225.78   4.377%   $235.6624   $235.66   $235.65   $235.70  
  7 purchase totals = $1,110.60       $1,206.0470   $1,206.06   $1,206.05   $1,206.10