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 $216.91   12.654%   $244.3578   $244.36   $244.35   $244.40  
  Purchase #2 $139.39   5.142%   $146.5574   $146.56   $146.55   $146.60  
  Purchase #3 $225.58   11.723%   $252.0247   $252.02   $252.00   $252.00  
  Purchase #4 $231.56   5.270%   $243.7632   $243.76   $243.75   $243.80  
  Purchase #5 $196.72   13.773%   $223.8142   $223.81   $223.80   $223.80  
  Purchase #6 $227.41   3.685%   $235.7901   $235.79   $235.80   $235.80  
  Purchase #7 $26.39   7.454%   $28.3571   $28.36   $28.35   $28.40  
  7 purchase totals = $1,263.96       $1,374.6645   $1,374.66   $1,374.60   $1,374.80