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 $212.27   11.852%   $237.4282   $237.43   $237.45   $237.40  
  Purchase #2 $23.32   4.654%   $24.4053   $24.41   $24.40   $24.40  
  Purchase #3 $65.53   4.197%   $68.2803   $68.28   $68.30   $68.30  
  Purchase #4 $245.78   7.288%   $263.6924   $263.69   $263.70   $263.70  
  Purchase #5 $35.33   3.221%   $36.468   $36.47   $36.45   $36.50  
  Purchase #6 $195.72   9.666%   $214.6383   $214.64   $214.65   $214.60  
  Purchase #7 $158.44   5.761%   $167.5677   $167.57   $167.55   $167.60  
  7 purchase totals = $936.39       $1,012.4802   $1,012.49   $1,012.50   $1,012.50