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 $130.96   11.682%   $146.2587   $146.26   $146.25   $146.30  
  Purchase #2 $232.99   4.302%   $243.0132   $243.01   $243.00   $243.00  
  Purchase #3 $196.94   3.619%   $204.0673   $204.07   $204.05   $204.10  
  Purchase #4 $227.91   3.272%   $235.3672   $235.37   $235.35   $235.40  
  Purchase #5 $91.69   3.611%   $95.0009   $95.00   $95.00   $95.00  
  Purchase #6 $203.32   11.380%   $226.4578   $226.46   $226.45   $226.50  
  Purchase #7 $177.71   11.648%   $198.4097   $198.41   $198.40   $198.40  
  7 purchase totals = $1,261.52       $1,348.5748   $1,348.58   $1,348.50   $1,348.70